mach: recreate .venv when .python-version changes (#34712)

The new images published in servo/ci-runners#12 should have `uv`
installed already and the initial build of servo triggered during the
base image construction will force the installation of the Python
version mentioned at the time of the image construction (3.12). When
.python-version changes, we can no longer use the .venv baked into the
image and must recreate the it to avoid activating the environment.

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

.github/workflows/windows.yml

@@ -115,16 +115,14 @@ jobs:
         run: |
           choco install wixtoolset
           echo "C:\\Program Files (x86)\\WiX Toolset v3.11\\bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
-      - uses: actions/setup-python@v5
       - name: Setup Python
+        if: ${{ runner.environment != 'self-hosted' }}
         uses: ./.github/actions/setup-python
-        with:
-          skip-python-setup: ${{ runner.environment == 'self-hosted' }}
       - name: Bootstrap
         if: ${{ runner.environment != 'self-hosted' }}
         run: |
-          python mach fetch
-          python mach bootstrap-gstreamer
+          .\mach fetch
+          .\mach bootstrap-gstreamer
       # For some reason WiX isn't currently on the GitHub runner path. This is a
       # temporary workaround until that is fixed.
       - name: Add WiX to Path
@@ -147,21 +145,21 @@ jobs:
 
       - name: Build (${{ inputs.profile }})
         run: |
-          python mach build --use-crown --locked --${{ inputs.profile }}
+          .\mach build --use-crown --locked --${{ inputs.profile }}
           cp C:\a\servo\servo\target\cargo-timings C:\a\servo\servo\target\cargo-timings-windows -Recurse
       - name: Copy resources
         if: ${{ runner.environment != 'self-hosted' }}
         # GitHub-hosted runners check out the repo on D: drive.
         run: cp D:\a\servo\servo\resources C:\a\servo\servo -Recurse
       - name: Smoketest
-        run: python mach smoketest --${{ inputs.profile }}
+        run: .\mach smoketest --${{ inputs.profile }}
       - name: Unit tests
         if: ${{ inputs.unit-tests }}
         uses: nick-fields/retry@v3
         with:
           timeout_minutes: 30
           max_attempts: 3 # https://github.com/servo/servo/issues/30683
-          command: python mach test-unit --${{ inputs.profile }} -- -- --test-threads=1
+          command: .\mach test-unit --${{ inputs.profile }} -- -- --test-threads=1
       - name: Archive build timing
         uses: actions/upload-artifact@v4
         with:
@@ -169,7 +167,7 @@ jobs:
           # Using a wildcard here ensures that the archive includes the path.
           path: C:\\a\\servo\\servo\\target\\cargo-timings-*
       - name: Build mach package
-        run: python mach package --${{ inputs.profile }}
+        run: .\mach package --${{ inputs.profile }}
       - name: Upload artifact for mach package
         uses: actions/upload-artifact@v4
         with:
@@ -182,7 +180,7 @@ jobs:
       - name: Upload nightly
         if: ${{ inputs.upload }}
         run: |
-          python mach upload-nightly windows-msvc --secret-from-environment `
+          .\mach upload-nightly windows-msvc --secret-from-environment `
             --github-release-id ${{ inputs.github-release-id }}
         env:
           S3_UPLOAD_CREDENTIALS: ${{ secrets.S3_UPLOAD_CREDENTIALS }}