Hithomelabs/CFTunnels#122: replace actions/setup-java@v4 with Alpine-native JDK install for ci-runner container

.gitea/workflows/test_image_build_push.yml

@@ -36,11 +36,10 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
-      - name: JDK setup
-        uses: actions/setup-java@v4
-        with:
-          distribution: 'zulu'
-          java-version: '17'
+      - name: Install JDK (Alpine package)
+        run: |
+          apk add --no-cache openjdk17-jdk
+          echo "JAVA_HOME=/usr/lib/jvm/java-17-openjdk" >> "$GITHUB_ENV"
       - name: Validate Gradle Wrapper
         uses: gradle/actions/wrapper-validation@v3
       - name: Create and push tag