Add CI check for Grep warnings

.gitlab-ci.yml

@@ -303,6 +303,7 @@ stages:
     - cd bin/tests/system
     - make -j${TEST_PARALLEL_JOBS:-1} -k check V=1
     - if git rev-parse > /dev/null 2>&1; then ( ! grep "^I:.*:file.*not removed$" *.log ); fi
+    - '( ! grep -F "grep: warning:" *.log )'
   after_script:
     - test -d bind-* && cd bind-*
     - REALSOURCEDIR="$PWD"