ci: simplifying tests for BOM (#2431)

* fix: add versions.txt to 6.0.x-lts branch

* ci: simplifying tests

Author: suztomo

.github/workflows/ci.yaml

@@ -20,8 +20,10 @@ jobs:
     # The http connection settings avoid Maven's HTTP connection reset in GitHub Actions
     # https://github.com/actions/virtual-environments/issues/1499#issuecomment-689467080
     - run: |
-        ./mvnw -B -e -ntp install \
+        ./mvnw -B -e -ntp test \
+            -pl dependencies,boms/integration-tests \
+            -DfailIfNoTests=false \
+            -Dtest=com.google.cloud.BomContentTest \
             -Dhttp.keepAlive=false -Dmaven.wagon.http.pool=false \
             -Dmaven.wagon.httpconnectionManager.ttlSeconds=120
-    - run: cd gradle-plugin && ./gradlew build publishToMavenLocal