`tests` are shipped as a module with the package

## What is the problem?

`tests` directory is shipped as part of the package. This can be a problem, since many projects contain a `tests` directory themselves. For example, this can be a problem for projects that import from their tests directory while running the tests. 
The reason for this is that the module `tests` is now ambiguous; it refers both to `tests` in the virtual environment, and to the `tests` directory in their project. This will lead to errors while running the unit tests like:

```
ModuleNotFoundError: No module named 'tests.utils'
```

The issue can be confirmed with the following steps:

```sh
pip download --no-deps --only-binary=:all: msal-extensions==1.3.0
unzip msal_extensions-1.3.0-py3-none-any.whl -d extracted_wheel
ls -1 extracted_wheel 
```

This shows the following directories exist in the wheel file:

```
msal_extensions
msal_extensions-1.3.0.dist-info 
tests
```

## How to solve this?

`tests` should not be shipped with the `msal-extensions` package. Probably the line `packages=find_packages()` in `setup.py` should be modified.

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