Diff tag are not reachable by keyboard

[dbaeumer]

Testing #250357

These tags are not reachable by keyboard.

[dbaeumer]

Actually they are clickable but not reachable by keyboard.

[justschen]

this is the case in stable as well actually hmmm

cc. @meganrogge idk if when the pills were added, if there was any talk about why these don't have a tab index?

[meganrogge]

Probably just an oversight. We should defintely add tab indices to them and nice aria labels

[meganrogge]

related #17563