Do not run ee_compat_check on security branches

Branches started from `security-X-Y` will likely fail on `ee_compat_check`,
the check tries to merge against EE `master` which may likely fail for MR that
are not targetted on `master`, like security fixes.

This commit disables `ee_compat_check` on branches starting with `security-`.

.gitlab-ci.yml

@@ -431,6 +431,7 @@ ee_compat_check:
     - master
     - tags
     - /^[\d-]+-stable(-ee)?/
+    - /^security-/
     - branches@gitlab-org/gitlab-ee
     - branches@gitlab/gitlab-ee
   retry: 0