Description:
Expose a python-path output containing the chosen Python executable path.

Related issue:
fix #309
mitigate #132

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

The failure for e2e-cache / Test poetry (Python pypy-3.7-v7.x, windows-latest) seems unrelated to changes in this PR.

Hi @mayeut, why you don't want to use pythonLocation environment variable for this purpose?

The output works doesn't rely on modifying the environment, and doesn't get overwritten. So you could do multiple setup-python's, and access the correct output. An example of this might be problematic:

- uses: actions/setup-python@v3
  with:
    python-version: "3.7"
- uses: some/composite-action@v1 # Runs a different setup-python internally
# Now pythonLocation is no longer the 3.7 one!

The failure for e2e-cache / Test poetry (Python pypy-3.7-v7.x, windows-latest) seems unrelated to changes in this PR.
(the previous failure on the same test went away with a relaunch of the workflow by @vsafonkin)