Include JUnit test output files in build log artifact uploaded to GCP (#55987)

gradle/build-complete.gradle

@@ -16,6 +16,7 @@ if (buildNumber) {
           Set<File> fileSet = fileTree(projectDir) {
             include("**/*.hprof")
             include("**/reaper.log")
+            include("**/build/test-results/**/*.xml")
             include("**/build/testclusters/**")
             exclude("**/build/testclusters/**/data/**")
             exclude("**/build/testclusters/**/distro/**")