ci: add TLS showcase server instance to dependency compatibility test workflow

Author: lqiu96

.github/workflows/sdk-platform-java-dependency_compatibility_test.yaml

@@ -90,7 +90,22 @@ jobs:
           curl --location https://github.com/googleapis/gapic-showcase/releases/download/v${SHOWCASE_VERSION}/gapic-showcase-${SHOWCASE_VERSION}-linux-amd64.tar.gz --output /usr/src/showcase/showcase-${SHOWCASE_VERSION}-linux-amd64.tar.gz
           cd /usr/src/showcase/
           tar -xf showcase-*
+          # Start standard insecure showcase server on default port 7469 for standard integration tests
           ./gapic-showcase run &
+          # Start secure TLS showcase server on port 7470 for PQC TLS integration tests
+          ./gapic-showcase run --port 7470 --tls --ca-cert-output-file /tmp/showcase-ca.pem &
+          # Wait deterministically for both background showcase servers to finish binding ports 7469/7470
+          # and writing /tmp/showcase-ca.pem. Starting TLS requires RSA key generation and disk I/O,
+          # which can cause race conditions if tests start before /tmp/showcase-ca.pem is created.
+          for i in $(seq 1 30); do
+            if (echo > /dev/tcp/127.0.0.1/7469) 2>/dev/null && \
+               (echo > /dev/tcp/127.0.0.1/7470) 2>/dev/null && \
+               [ -f /tmp/showcase-ca.pem ]; then
+              echo "Showcase servers (ports 7469, 7470) and CA cert ready in attempt $i."
+              break
+            fi
+            sleep 0.2
+          done
           cd -
         working-directory: sdk-platform-java