[REFACTOR] github actions Docker 이미지 캐싱 여부 확인 및 개선

.github/workflows/ci.yml

@@ -18,6 +18,39 @@ jobs:
       - name: Repository Checkout
         uses: actions/checkout@v4
 
+      # --- Testcontainers Docker image cache (mysql + ryuk) ---
+      - name: Create docker cache directory
+        run: mkdir -p /tmp/docker-cache
+
+      - name: Cache Testcontainers images
+        id: tc-image-cache
+        uses: actions/cache@v4
+        with:
+          path: /tmp/docker-cache
+          key: testcontainers-images-${{ runner.os }}-mysql8.0-ryuk0.12.0-v1
+          restore-keys: |
+            testcontainers-images-${{ runner.os }}-
+
+      - name: Pull and save Docker images (cache miss)
+        if: steps.tc-image-cache.outputs.cache-hit != 'true'
+        run: |
+          set -euo pipefail
+
+          docker pull mysql:8.0
+          docker save -o /tmp/docker-cache/mysql_8.0.tar mysql:8.0
+
+          docker pull testcontainers/ryuk:0.12.0
+          docker save -o /tmp/docker-cache/ryuk_0.12.0.tar testcontainers/ryuk:0.12.0
+
+      - name: Load cached Docker images (cache hit)
+        if: steps.tc-image-cache.outputs.cache-hit == 'true'
+        run: |
+          set -euo pipefail
+
+          docker load -i /tmp/docker-cache/mysql_8.0.tar
+          docker load -i /tmp/docker-cache/ryuk_0.12.0.tar
+      # --- End Testcontainers Docker image cache ---
+
       - name: Set up JDK 21
         uses: actions/setup-java@v4
         with: