1.0.2: create temp directory in source tree trashes build

Looks like some bits may be still missing on pyproject.toml.

Here is test case:

```console

+ cd uc.micro-py-1.0.2

+ mkdir temp

+ /usr/bin/python3 -sBm build -w --no-isolation

* Getting build dependencies for wheel...

No `packages` or `py_modules` configuration, performing automatic discovery.

`flat-layout` detected -- analysing .

discovered packages -- ['uc_micro', 'temp', 'uc_micro.categories', 'uc_micro.properties', 'uc_micro.categories.Cc', 'uc_micro.categories.Cf', 'uc_micro.categories.P', 'uc_micro.categories.Z', 'uc_micro.properties.Any']

Traceback (most recent call last):

  File "/usr/lib/python3.8/site-packages/pyproject_hooks/_in_process/_in_process.py", line 353, in <module>

    main()

  File "/usr/lib/python3.8/site-packages/pyproject_hooks/_in_process/_in_process.py", line 335, in main

    json_out['return_val'] = hook(**hook_input['kwargs'])

  File "/usr/lib/python3.8/site-packages/pyproject_hooks/_in_process/_in_process.py", line 118, in get_requires_for_build_wheel

    return hook(config_settings)

  File "/usr/lib/python3.8/site-packages/setuptools/build_meta.py", line 325, in get_requires_for_build_wheel

    return self._get_build_requires(config_settings, requirements=['wheel'])

  File "/usr/lib/python3.8/site-packages/setuptools/build_meta.py", line 295, in _get_build_requires

    self.run_setup()

  File "/usr/lib/python3.8/site-packages/setuptools/build_meta.py", line 311, in run_setup

    exec(code, locals())

  File "<string>", line 1, in <module>

  File "/usr/lib/python3.8/site-packages/setuptools/__init__.py", line 103, in setup

    return distutils.core.setup(**attrs)

  File "/usr/lib/python3.8/site-packages/setuptools/_distutils/core.py", line 159, in setup

    dist.parse_config_files()

  File "/usr/lib/python3.8/site-packages/setuptools/dist.py", line 627, in parse_config_files

    pyprojecttoml.apply_configuration(self, filename, ignore_option_errors)

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 66, in apply_configuration

    config = read_configuration(filepath, True, ignore_option_errors, dist)

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 131, in read_configuration

    return expand_configuration(asdict, root_dir, ignore_option_errors, dist)

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 156, in expand_configuration

    return _ConfigExpander(config, root_dir, ignore_option_errors, dist).expand()

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 204, in expand

    self._expand_all_dynamic(dist, package_dir)

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 249, in _expand_all_dynamic

    version=self._obtain_version(dist, package_dir),

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 298, in _obtain_version

    return _expand.version(self._obtain(dist, "version", package_dir))

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 287, in _obtain

    return self._expand_directive(

  File "/usr/lib/python3.8/site-packages/setuptools/config/pyprojecttoml.py", line 281, in _expand_directive

    return _expand.read_attr(directive["attr"], package_dir, root_dir)

  File "/usr/lib/python3.8/site-packages/setuptools/config/expand.py", line 188, in read_attr

    _parent_path, path, module_name = _find_module(module_name, package_dir, root_dir)

  File "/usr/lib/python3.8/site-packages/setuptools/config/expand.py", line 229, in _find_module

    if package_dir:

  File "/usr/lib/python3.8/site-packages/setuptools/config/expand.py", line 459, in __len__

    return len(self._target())

  File "/usr/lib/python3.8/site-packages/setuptools/config/expand.py", line 452, in _target

    self._value = self._obtain()

  File "/usr/lib/python3.8/site-packages/setuptools/config/expand.py", line 422, in _get_package_dir

    self()

  File "/usr/lib/python3.8/site-packages/setuptools/config/expand.py", line 412, in __call__

    self._dist.set_defaults(name=False)  # Skip name, we can still be parsing

  File "/usr/lib/python3.8/site-packages/setuptools/discovery.py", line 353, in __call__

    self._analyse_package_layout(ignore_ext_modules)

  File "/usr/lib/python3.8/site-packages/setuptools/discovery.py", line 387, in _analyse_package_layout

    or self._analyse_flat_layout()

  File "/usr/lib/python3.8/site-packages/setuptools/discovery.py", line 444, in _analyse_flat_layout

    return self._analyse_flat_packages() or self._analyse_flat_modules()

  File "/usr/lib/python3.8/site-packages/setuptools/discovery.py", line 450, in _analyse_flat_packages

    self._ensure_no_accidental_inclusion(top_level, "packages")

  File "/usr/lib/python3.8/site-packages/setuptools/discovery.py", line 480, in _ensure_no_accidental_inclusion

    raise PackageDiscoveryError(cleandoc(msg))

setuptools.errors.PackageDiscoveryError: Multiple top-level packages discovered in a flat-layout: ['uc_micro', 'temp'].



To avoid accidental inclusion of unwanted files or directories,

setuptools will not proceed with this build.



If you are trying to create a single distribution with multiple packages

on purpose, you should not rely on automatic discovery.

Instead, consider the following options:



1. set up custom discovery (`find` directive with `include` or `exclude`)

2. use a `src-layout`

3. explicitly set `py_modules` or `packages` with a list of names



To find more information, look for "package discovery" on setuptools docs.



ERROR Backend subprocess exited when trying to invoke get_requires_for_build_wheel

```

[]