Add CI job for tag validation

Release v5.11.12.1-1 was accidentally created instead of v5.11.12.0-1: #1287 (closed)

We should have a job that checks the validity of the tag you are trying to create to prevent these errors in the future.

For any new tag, it should check that there was a valid tag before it. Some examples:

• v5.11.12.1-2 can only be created if v5.11.12.1-1 exists
• v5.11.12.1-1 can only be created if v5.11.12.0-* exists
• v5.11.12.0-1 can only be created if v5.11.11.* exists
• v5.12.0.0-1 can only be created if v5.11.* exists
• v6.12.0.0-1 can only be created if v5.* exists

This check should be part of the changelog generation and the tag pipelines.