Do not allow extending enums for CI
I noticed an MR !8469 (merged) that allows making enums easily extendable for EE, by reducing conflicts related to that.
This, in general, is a good idea, but I think that we should disallow such behavior at least for CI. We had cases in past when added enum (on EE) had the next index to CE, thus anyone adding then enum to CE would have to remember that there's no clash of enums values.
The need for backporting such enum adds slightly more effort, but the minimal amount, but ensures that we keep consistency what values are being used.
We do that already in other places (artifacts), we simply backport enum values. It is simpler, even though we do not use them directly in CE codebase.