CI: disable fail-fast and add deb maker diagnostic

.github/workflows/build.yml

@@ -27,6 +27,7 @@ jobs:
     name: Build (${{ matrix.os }} - ${{ matrix.arch }})
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: false
       matrix:
         # Build for supported platforms
         # https://github.com/electron/electron-packager/blob/ebcbd439ff3e0f6f92fa880ff28a8670a9bcf2ab/src/targets.js#L9
@@ -78,6 +79,9 @@ jobs:
           DISK_URL: ${{ secrets.DISK_URL }}
       - name: Install
         run: npm ci
+      - name: Diagnose deb maker
+        if: matrix.os == 'ubuntu-latest'
+        run: node -e "try{require('electron-installer-debian');console.log('deb installer OK')}catch(e){console.error(e)}"
       - name: Make
         if: startsWith(github.ref, 'refs/tags/')
         run: npm run make -- --arch=${{ matrix.arch }}