verify CI fails when build fails with proguard tests enabled

Author: demolaf

scripts/build.sh

@@ -9,6 +9,6 @@ cp library/google-services.json proguard-tests/google-services.json
 ./gradlew $GRADLE_ARGS clean
 ./gradlew $GRADLE_ARGS assembleDebug
 # TODO(thatfiredev): re-enable before release
-#./gradlew $GRADLE_ARGS proguard-tests:build
+./gradlew $GRADLE_ARGS proguard-tests:build
 ./gradlew $GRADLE_ARGS checkstyle 
 ./gradlew $GRADLE_ARGS testDebugUnitTest