Wrong entry-point fix_random_seed

Following #747, PR #748 was merged, but there's a typo in the entrypoint: it should be `thinc.api:fix_random_seed` instead of `thinc.api.fix_random_seed` (colon instead of dot to separate module and function).



This result in such a traceback when running pytest with pytest-randomly enabled:



```python

pytest -c config/pytest.ini -n auto -k "" tests

  ============================= test session starts ==============================

  platform linux -- Python 3.8.11, pytest-7.1.3, pluggy-1.0.0

  INTERNALERROR> Traceback (most recent call last):

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/_pytest/main.py", line 266, in wrap_session

  INTERNALERROR>     config.hook.pytest_sessionstart(session=session)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_hooks.py", line 265, in __call__

  INTERNALERROR>     return self._hookexec(self.name, self.get_hookimpls(), kwargs, firstresult)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_manager.py", line 80, in _hookexec

  INTERNALERROR>     return self._inner_hookexec(hook_name, methods, kwargs, firstresult)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_callers.py", line 60, in _multicall

  INTERNALERROR>     return outcome.get_result()

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_result.py", line 60, in get_result

  INTERNALERROR>     raise ex[1].with_traceback(ex[2])

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_callers.py", line 39, in _multicall

  INTERNALERROR>     res = hook_impl.function(*args)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/_pytest/terminal.py", line 710, in pytest_sessionstart

  INTERNALERROR>     lines = self.config.hook.pytest_report_header(

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/_pytest/config/compat.py", line 67, in fixed_hook

  INTERNALERROR>     return hook(**kw)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_hooks.py", line 265, in __call__

  INTERNALERROR>     return self._hookexec(self.name, self.get_hookimpls(), kwargs, firstresult)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_manager.py", line 80, in _hookexec

  INTERNALERROR>     return self._inner_hookexec(hook_name, methods, kwargs, firstresult)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_callers.py", line 60, in _multicall

  INTERNALERROR>     return outcome.get_result()

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_result.py", line 60, in get_result

  INTERNALERROR>     raise ex[1].with_traceback(ex[2])

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pluggy/_callers.py", line 39, in _multicall

  INTERNALERROR>     res = hook_impl.function(*args)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pytest_randomly/__init__.py", line 188, in pytest_report_header

  INTERNALERROR>     _reseed(config)

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pytest_randomly/__init__.py", line 170, in _reseed

  INTERNALERROR>     entrypoint_reseeds = [e.load() for e in eps]

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/pytest_randomly/__init__.py", line 170, in <listcomp>

  INTERNALERROR>     entrypoint_reseeds = [e.load() for e in eps]

  INTERNALERROR>   File "/home/user/project/tests/tmp/__pypackages__/3.8/lib/importlib_metadata/__init__.py", line 203, in load

  INTERNALERROR>     module = import_module(match.group('module'))

  INTERNALERROR>   File "/home/user/.basher-packages/pyenv/pyenv/versions/3.8.11/lib/python3.8/importlib/__init__.py", line 127, in import_module

  INTERNALERROR>     return _bootstrap._gcd_import(name[level:], package, level)

  INTERNALERROR>   File "<frozen importlib._bootstrap>", line 1014, in _gcd_import

  INTERNALERROR>   File "<frozen importlib._bootstrap>", line 991, in _find_and_load

  INTERNALERROR>   File "<frozen importlib._bootstrap>", line 970, in _find_and_load_unlocked

  INTERNALERROR> ModuleNotFoundError: No module named 'thinc.api.fix_random_seed'; 'thinc.api' is not a package

```

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