ci: Fail on any common lint errors

Now that we fixed all pre-existing errors that are common between
regular and legacy configuration, we can stop filtering the result
by the lines modified by the merge request.

This will allow us to catch errors in merge requests that slipped
through until now, for example when leaving a newly-unused import
behind.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/716

.gitlab-ci/run-eslint.sh

@@ -86,9 +86,13 @@ run_eslint LEGACY
 echo Done.
 create_common
 
+if ! is_empty $OUTPUT_FINAL; then
+  cat $OUTPUT_FINAL
+  exit 1
+fi
+
 # Just show the report and succeed when not testing a MR
 if [ -z "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" ]; then
-  cat $OUTPUT_FINAL
   exit 0
 fi