Cache .deb for libffi instead of always downloading (#30142)

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

.github/workflows/linux-wpt.yml

@@ -39,6 +39,16 @@ jobs:
         with:
           name: release-binary
           path: release-binary
+      - name: Cache libffi
+        id: cache
+        uses: actions/cache@v3
+        with:
+          path: ./libffi6_3.2.1-8_amd64.deb
+          key: cache-libffi
+      - name: Download libffi
+        if: steps.cache.outputs.cache-hit != 'true'
+        run: |
+          wget http://mirrors.kernel.org/ubuntu/pool/main/libf/libffi/libffi6_3.2.1-8_amd64.deb
       - name: unPackage binary
         run: tar -xzf release-binary/target.tar.gz
       - name: Prep test environment
@@ -46,7 +56,6 @@ jobs:
           python3 -m pip install --upgrade pip virtualenv
           sudo apt update
           sudo apt install -qy --no-install-recommends libgl1 libssl1.1 libdbus-1-3 libxcb-xfixes0-dev libxcb-shape0-dev libunwind8 libegl1-mesa
-          wget http://mirrors.kernel.org/ubuntu/pool/main/libf/libffi/libffi6_3.2.1-8_amd64.deb
           sudo apt install ./libffi6_3.2.1-8_amd64.deb
           python3 ./mach bootstrap-gstreamer
       - name: Sync from upstream WPT