Switch buildx driver on PRs so locally built image is used

Author: LegNeato

.github/workflows/container_images.yml

@@ -143,6 +143,8 @@ jobs:
     name: Build ${{ matrix.variance.name }} (${{ matrix.platform.arch }})
     needs: build-toolchain
     runs-on: ${{ matrix.platform.runner }}
+    env:
+      BUILDX_DRIVER: ${{ github.event_name == 'pull_request' && 'docker' || 'docker-container' }}
     permissions:
       contents: read
       packages: write
@@ -227,6 +229,8 @@ jobs:
           df -h
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
+        with:
+          driver: ${{ env.BUILDX_DRIVER }}
       - name: Prepare BuildKit temp space
         run: |
           mkdir -p "${{ runner.temp }}/buildkit-tmp"