Add a CI job for creating SRCINFO for all packages in the repo

It caches them on a github release and updates them as the repo changes.

This will be used by packages.msys2.org to show the content of the repo.

.github/workflows/generate-srcinfo.yml

@@ -0,0 +1,48 @@
+name: generate-srcinfo
+
+on:
+  push:
+    branches:
+      - master
+  workflow_dispatch:
+
+jobs:
+  update-srcinfo:
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      - uses: msys2/setup-msys2@v2
+        with:
+          msystem: MSYS
+          install: python git mingw-w64-x86_64-toolchain mingw-w64-i686-toolchain
+          update: true
+
+      - run: |
+          curl -L --retry 5 -o srcinfo.json "https://github.com/$GITHUB_REPOSITORY/releases/download/srcinfo-cache/srcinfo.json"
+          python ci-generate-srcinfo.py --time-limit 19800 mingw . srcinfo.json
+
+      - uses: actions/upload-artifact@v2
+        with:
+          name: result
+          path: srcinfo.json
+
+  upload-srcinfo:
+    needs: update-srcinfo
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/download-artifact@v2
+        with:
+          name: result
+
+      - uses: eine/tip@master
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          tag: srcinfo-cache
+          rm: true
+          files: srcinfo.json