gha/test-validate: Reuse the dev image

Don't build the dev image separately for each validation.

Build it once and then cache it so the validations can reuse it.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

.github/workflows/test.yml

@@ -67,7 +67,14 @@ jobs:
           set: |
             *.cache-from=type=gha,scope=dev${{ matrix.mode }}
             *.cache-to=type=gha,scope=dev${{ matrix.mode }}
-            *.output=type=cacheonly
+            ${{ matrix.mode == '' && '*.output=type=docker,dest=/tmp/dev-image.tar' || '*.output=type=cacheonly' }}
+      -
+        name: Cache dev image
+        if: matrix.mode == ''
+        uses: actions/cache/save@v4
+        with:
+          key: dev-image-${{ github.run_id }}
+          path: /tmp/dev-image.tar
 
   test:
     if: ${{ github.event_name != 'pull_request' || !contains(github.event.pull_request.labels.*.name, 'ci/validate-only') }}
@@ -122,7 +129,6 @@ jobs:
       - validate-prepare
       - build-dev
     strategy:
-      fail-fast: false
       matrix:
         script: ${{ fromJson(needs.validate-prepare.outputs.matrix) }}
     steps:
@@ -139,15 +145,19 @@ jobs:
         uses: docker/setup-buildx-action@v3
         with:
           version: ${{ env.SETUP_BUILDX_VERSION }}
-          driver-opts: image=${{ env.SETUP_BUILDKIT_IMAGE }}
+          driver: docker
           buildkitd-flags: --debug
       -
-        name: Build dev image
-        uses: docker/bake-action@v6
+        name: Restore dev image
+        uses: actions/cache/restore@v4
         with:
-          targets: dev
-          set: |
-            dev.cache-from=type=gha,scope=dev
+          key: dev-image-${{ github.run_id }}
+          path: /tmp/dev-image.tar
+          fail-on-cache-miss: true
+      -
+        name: Load dev image
+        run: |
+          docker load -i /tmp/dev-image.tar
       -
         name: Validate
         run: |