Allow schema validation job failure for exit code 128

git diff A...B is equivalent to git diff $(git merge-base A B) B.
See man git-diff.

In some special situations `git merge-base A B` fails with "fatal: FETCH_HEAD...HEAD: no merge base".

.gitlab-ci.yml

@@ -93,6 +93,8 @@ schema validation:
     - pipelines
     - schedules
     - triggers
+  allow_failure:
+    exit_codes: 128
   before_script:
     - apk add git
     - npm -g install ajv-cli