Remove redundant Docker build test job

The test-docker-build job is unnecessary because the test-local-action
job already builds the Docker image for each test case when using 'uses: ./'.
This reduces CI time and eliminates redundancy.

Author: claude

.github/workflows/test-action.yml

@@ -48,23 +48,3 @@ jobs:
           PHP_VERSION: ${{ matrix.test_case.php_version }}
         with:
           args: ${{ matrix.test_case.args }}
-
-  test-docker-build:
-    name: Test Docker Build
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
-      - name: Build Docker image
-        uses: docker/build-push-action@v5
-        with:
-          context: .
-          push: false
-          tags: phparkitect/arkitect-github-actions:test
-          cache-from: type=gha
-          cache-to: type=gha,mode=max