Allow installation of extras in GitHub action

[ofek]

When setting the build-frontend to build[uv] one must manually make UV globally available on Windows and macOS. This leads to conditional execution as seen in this snippet of real CI configuration:

    - name: Download source distribution
      uses: actions/download-artifact@v4
      with:
        name: artifact-sdist
        path: dist

    - name: Install UV
      if: runner.os != 'Linux'
      uses: astral-sh/setup-uv@v6

    - name: Build wheels
      uses: pypa/cibuildwheel@v3.2.1
      with:
        package-dir: dist/${{ needs.sdist.outputs.sdist-name }}

Such an option would allow for removing the middle step:

    - name: Download source distribution
      uses: actions/download-artifact@v4
      with:
        name: artifact-sdist
        path: dist

    - name: Build wheels
      uses: pypa/cibuildwheel
      with:
        extras: uv
        package-dir: dist/${{ needs.sdist.outputs.sdist-name }}

Here's a PR to showcase this change being successfully used.

[joerick]

thanks! just wondering if we can simplify a little.

[joerick]

thank you for putting this together @ofek ! A nice improvement for sure.