Prevent creating branches other than main

From the comments:

I can't wrap my mind around 10 people pushing changes to main all the time. It feels like a merge-conflict-rollback-preventing nightmare to me.

That's ... literally what one of my colleagues is unironically advocating for over a decade. Despite us trying to explain to him that this might work for team of 2-3 people but is really a bad idea for team of 10+ developers, 5 or so testers, POs needing guarantee that they can deploy at any time and tools like Gitlab/Github. Thankfully we overruled him few years ago