fix: speed up integration tests with more caching

.github/workflows/integration.yml

@@ -15,6 +15,24 @@ jobs:
         uses: actions/checkout@v3
       - name: Init Hermit
         uses: cashapp/activate-hermit@v1
+      - name: Cache Go Modules
+        id: cache-go-modules
+        uses: actions/cache@v3
+        with:
+          path: ~/go/pkg/mod
+          key: ${{ runner.os }}-go
+      - name: Build Kotlin Echo
+        uses: gradle/gradle-build-action@v2
+        with:
+          arguments: build
+          build-root-directory: examples/echo-kotlin
+          gradle-executable: ${{ github.workspace }}/bin/gradle
+      - name: Build Kotlin Runtime
+        uses: gradle/gradle-build-action@v2
+        with:
+          arguments: build
+          build-root-directory: kotlin-runtime/ftl-runtime
+          gradle-executable: ${{ github.workspace }}/bin/gradle
       - name: Docker Compose
         run: docker compose up -d --wait
       - name: Integration tests