tests: Update CI to enable showcase profile.

Author: blakeli0

.github/workflows/ci.yaml

@@ -306,7 +306,7 @@ jobs:
       - name: Showcase integration tests - protobuf-3.25.8
         working-directory: java-showcase
         run: |
-          mvn clean verify -P '!showcase,enable-integration-tests,protobuf-3.25.8'  \
+          mvn clean verify -P 'enable-integration-tests,protobuf-3.25.8'  \
             --batch-mode \
             --no-transfer-progress
   showcase: