Enable creation of venv with existing python version

[xmatthias]

the FAQ specifically mentions:

Using actions/setup-python can be faster, because GitHub caches the Python versions alongside the runner.

So as a consequence - i'm trying to use that - but use the astral-sh/setup-uv function to install UV.
Unfortunately, there seems to be no way to have uv setup a virtual environment - all while reusing the existing python installation.

The only way i found was through passing in python-version: ${{ matrix.python-version }} - but that installs a 2nd copy of python alongside the one installed via actions/setup-python - so contradicts the above FAQ entry (i could remove the setup-python action as it's python ain't used).

    - name: Set up Python
      uses: actions/setup-python@v5
      with:
        python-version: ${{ matrix.python-version }}

    - name: Install uv
      uses: astral-sh/setup-uv@v5
      with:
        python-version: ${{ matrix.python-version }}

current workaround

(note: the below is for the windows variant - others will need slightly different workarounds)

    - name: Set up Python
      uses: actions/setup-python@v5
      with:
        python-version: ${{ matrix.python-version }}

    - name: Install uv
      uses: astral-sh/setup-uv@v5

    - name: Installation
      run: |
        uv venv
        .venv\Scripts\activate
        # persist the venv path for future steps
        "$(pwd)/.venv/Scripts" >> $env:GITHUB_PATH
 ... 

Desired solution:
A flag/parameter to allow UV to use the existing python installed via setup-python - but still do the venv magic (create venv, aktivate for the rest of the job, caching, ...)

    - name: Set up Python
      uses: actions/setup-python@v5
      with:
        python-version: ${{ matrix.python-version }}

    - name: Install uv
      uses: astral-sh/setup-uv@v5
      with:
        create-venv: true