🧪💅 Integrate build_msi into main CI workflow

Previously, this workflow would run on related file changes and not
contribute the the overall outcome of the CI run. This patch turns it
into a reusable workflow, integrating it closer with the rest of the
setup. It remains non-voting and skips or failures will not block the
CI, just as before.

.github/workflows/build.yml

@@ -48,6 +48,7 @@ jobs:
       #   }}
       #
       run-docs: ${{ steps.docs-changes.outputs.run-docs || false }}
+      run-win-msi: ${{ steps.win-msi-changes.outputs.run-win-msi || false }}
       run_tests: ${{ steps.check.outputs.run_tests || false }}
       run_hypothesis: ${{ steps.check.outputs.run_hypothesis || false }}
       run_cifuzz: ${{ steps.check.outputs.run_cifuzz || false }}
@@ -123,6 +124,20 @@ jobs:
         id: docs-changes
         run: |
           echo "run-docs=true" >> "${GITHUB_OUTPUT}"
+      - name: Get a list of the MSI installer-related files
+        id: changed-win-msi-files
+        uses: Ana06/get-changed-files@v2.3.0
+        with:
+          filter: |
+            Tools/msi/**
+            .github/workflows/reusable-windows-msi.yml
+          format: csv  # works for paths with spaces
+      - name: Check for docs changes
+        if: >-
+          steps.changed-win-msi-files.outputs.added_modified_renamed != ''
+        id: win-msi-changes
+        run: |
+          echo "run-win-msi=true" >> "${GITHUB_OUTPUT}"
 
   check-docs:
     name: Docs
@@ -218,6 +233,21 @@ jobs:
       arch: ${{ matrix.arch }}
       free-threading: ${{ matrix.free-threading }}
 
+  build_windows_msi:
+    name: >-  # ${{ '' } is a hack to nest jobs under the same sidebar category
+      📦 Windows MSI${{ '' }}
+    needs: check_source
+    if: fromJSON(needs.check_source.outputs.run-win-msi)
+    strategy:
+      matrix:
+        arch:
+        - x86
+        - x64
+        - arm64
+    uses: ./.github/workflows/reusable-windows-msi.yml
+    with:
+      arch: ${{ matrix.arch }}
+
   build_macos:
     name: 'macOS'
     needs: check_source
@@ -582,6 +612,7 @@ jobs:
     - build_ubuntu_ssltests
     - build_wasi
     - build_windows
+    - build_windows_msi
     - test_hypothesis
     - build_asan
     - build_tsan
@@ -596,6 +627,7 @@ jobs:
       with:
         allowed-failures: >-
           build_ubuntu_ssltests,
+          build_windows_msi,
           cifuzz,
           test_hypothesis,
         allowed-skips: >-

.github/workflows/reusable-windows-msi.yml

@@ -0,0 +1,24 @@
+name: TestsMSI
+
+on:
+  workflow_call:
+    inputs:
+      arch:
+        description: CPU architecture
+        required: true
+        type: string
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    name: installer for ${{ inputs.arch }}
+    runs-on: windows-latest
+    timeout-minutes: 60
+    env:
+      IncludeFreethreaded: true
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build CPython installer
+      run: .\Tools\msi\build.bat --doc -${{ inputs.arch }}