ci: try another version to reverse the grep result

.gitlab-ci.yml

@@ -32,7 +32,7 @@ test_benchmark:
   script:
     - docker pull $CONTAINER_TEST_IMAGE
     - docker run $CONTAINER_TEST_IMAGE /ttc18/gradlew benchmarkFull -Pscenario=0,small 2>&1 | tee benchmarkFull.log
-    - ! grep "BUILD FAILED" benchmarkFull.log
+    - grep "BUILD FAILED" benchmarkFull.log; test $? -eq 1
 
 test_unit_tests:
   stage: test