Only Assigning on Specified Branches

[ScarVite]

Is your feature request related to a problem? Please describe.
Yes, we are Using Branch protection Rules on master, but not on branch X.
However, we want to have somebody assigned, whenever a PR is made into branch X, but we don't want them to be assigned when merging into Master, as only a handful are allowed to push into master and it's just nerve wracking, to remove them every time, we open a pr to master,

Describe the solution you'd like
If i were to merge foo into bar and i've specified that the Bot should assign myself and user x, as reviewers when merging into bar, the bot should assign me and user x.
However, if i want to merge into master, the Bot isn't going to do anything, as i didn't Specifiy it.

Describe alternatives you've considered
Enabling Branch Protection Rules on branch X aswell, but this restricts our team from pushing into that branch directly, as a review is required.