Install Python 3.9 on 6.1 and lower

The underlying Windows image has been updated to remove Python 3.9.
Swift toolchains version 6.1 and lower require Python 3.9. Install it
for these toolchains, and continue to install 3.10 for toolchains > 6.1.

Author: plemarquand

.github/workflows/swift_package_test.yml

@@ -730,11 +730,17 @@ jobs:
           docker pull $Image
           echo "image=$Image" >> "$env:GITHUB_OUTPUT"
       - name: "Install Python 3.10"
-        if: ${{ !inputs.enable_windows_docker }}
+        if: ${{ !inputs.enable_windows_docker && !(matrix.swift_version == '6.1' || matrix.swift_version == '6.0' || matrix.swift_version == '5.10' || matrix.swift_version == '5.9') }}
         uses: actions/setup-python@v6
         with:
           python-version: "3.10"
           architecture: "x64"
+      - name: "Install Python 3.9"
+        if: ${{ !inputs.enable_windows_docker && (matrix.swift_version == '6.1' || matrix.swift_version == '6.0' || matrix.swift_version == '5.10' || matrix.swift_version == '5.9') }}
+        uses: actions/setup-python@v6
+        with:
+          python-version: "3.9"
+          architecture: "x64"
       - name: Install Visual Studio Build Tools
         if: ${{ !inputs.enable_windows_docker }}
         run: . ${{ steps.script_path.outputs.root }}/.github/workflows/scripts/windows/install-vsb.ps1
@@ -789,3 +795,4 @@ jobs:
         timeout-minutes: 60
         if: ${{ !inputs.enable_windows_docker }}
         run: powershell.exe -NoLogo -File $env:TEMP\test-script\run.ps1; exit $LastExitCode
+