Protect master branch

[giltho]

Hello,

I accidentally pushed to master something that I intended to push on my own fork...
I really apologise for this, I should have been more careful.
I reverted the commit, but it could be worth protecting the main branch to avoid future mistakes.

Also, I believe that my writing rights can be removed from the repository, since I do not know the codebase sufficiently anymore.

Cheers!

(+ what I pushed was compatibility with yojson 3.0, but there's already #1534)