Check for "file not removed" in system test output

Run this check only when in Git repository, because run.sh produces the
"file not removed" warnings only when in Git repository.

(cherry picked from commit 4a2778abdf)

.gitlab-ci.yml

@@ -292,6 +292,7 @@ stages:
   script:
     - ( cd bin/tests/system && make -j${TEST_PARALLEL_JOBS:-1} -k test V=1 )
     - test -s bin/tests/system/systests.output
+    - if git rev-parse > /dev/null 2>&1; then ( ! grep "^I:.*:file.*not removed$" bin/tests/system/systests.output ); fi
 
 .system_test: &system_test_job
   <<: *system_test_common