SCORU: Prohibit publishing commit with inbox level exceeding current

Context

We want to prohibit publishing commits with an inbox level greater than the current level.
It prevents malicious misbehavior.

Manually testing the MR

Added 2 regression tests.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Provide automatic testing (see the testing guide).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR