Don't push/import a commit to a repo if no changes occurred

[nazunalika]

srpmproc will push new commits, even if empty, to a repository. this is sometimes annoying, because it doesn't make it clear to the user if it was already imported at some point in the past. There should be a way for it to see that the repo it is importing to (assuming it is exists) has the same content with no changes occurring with its import (post-patch, if applicable), notify the user, and exit cleanly.

[lecler-i]

This is my take at it https://github.com/rocky-linux/srpmproc/compare/main...lecler-i:srpmproc:tweak/13-no-change-no-publish?expand=1

It just works, I didn't try any edge-cases tho, just to launch an repo sync multiple time in a row with no changes to my upstream