Create Test for validating the requirements.txt

[DavidoTek]

Create a new workflow to validate whether all entries in requirements.txt are correct.

For example, the build for commit 058b83d failed because steam@master required vdf.git@v4.0 and the requirements file also contained vdf@master which caused a conflict.

[sonic2kk]

This should be straightforward to add based on GitHub's Building and testing Python docs. They have a specific snippet for running requirements.txt.

We would probably want a workflow that attempts to run pip install -r requirements.txt. In future, if we have a specific tests/requirements.txt, we could include testing this in the same CI (using tests/requirements.txt may be a desirable way to install PyTest and any future libraries in CI without doing it manually like we do now).