ci: offer to build the full matrix of supported flavors

This lets us build some confidence whenever making big changes.

It has to be triggered manually because it is actually quite expensive
to run, therefore I want people to choose wisely whether or not to spend
the electricity.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/matrix.yml

@@ -0,0 +1,37 @@
+name: 'test all artifact flavors'
+on: # since this is expensive, require a manual trigger
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: windows-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        flavor: ['minimal', 'makepkg-git', 'build-installers', 'full']
+        architecture: ['i686', 'x86_64']
+        exclude:
+          - flavor: minimal
+            architecture: i686
+          - flavor: makepkg-git
+            architecture: i686
+    steps:
+      - uses: actions/checkout@v3
+      - name: run in-place
+        uses: ./
+        with:
+          flavor: ${{ matrix.flavor }}
+          architecture: ${{ matrix.architecture }}
+      - name: build installer
+        if: matrix.flavor == 'build-installers'
+        shell: bash
+        run: |
+          # clone build-extra
+          git clone --depth 1 --single-branch -b main https://github.com/git-for-windows/build-extra &&
+          # build installer
+          ./build-extra/installer/release.sh --output=$PWD/installer-${{ matrix.architecture }} 0-test
+      - uses: actions/upload-artifact@v2
+        if: matrix.flavor == 'build-installers'
+        with:
+          name: installer-${{ matrix.architecture }}
+          path: installer-${{ matrix.architecture }}