Add a job for a fast CI build

.github/workflows/ci.yml

@@ -8,6 +8,45 @@ permissions: read-all
 
 jobs:
 
+  fastbuild:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 60
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+    - uses: cachix/install-nix-action@v25
+      with:
+        # The sandbox would otherwise be disabled by default on Darwin
+        extra_nix_config: "sandbox = true"
+    - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
+    - uses: cachix/cachix-action@v14
+      if: needs.check_secrets.outputs.cachix == 'true'
+      with:
+        name: '${{ env.CACHIX_NAME }}'
+        signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - name: cache ccache files
+      uses: actions/cache@v4
+      with:
+        path: ~/.ccache
+        key: ${{ matrix.os }}-ccache-${{ github.run_number }}
+        restore-keys: |
+          ${{ matrix.os }}-ccache-
+    - run: |
+        export CCACHE_BASEDIR=$PWD
+        nix --experimental-features 'nix-command flakes' develop .\#native-ccacheStdenvPackages \
+          --command bash -c "
+            autoreconf -vfi &&
+            ./configure \$configureFlags --prefix=$PWD/outputs &&
+            make install OPTIMIZE=0 -j$(nproc) &&
+            make installcheck -j$(nproc)
+        "
+
   tests:
     needs: [check_secrets]
     strategy: