R1:10966519e2eb

Prevent "commit message magic words" parser from exploding on "reverts aaaa.....aaz"

Summary:
Fixes T9268. Currently, we try to match any string like "a2f313f1" as a commit/revision, so short hashes will get picked up.

However, we don't require a word boundary or terminal after the match, so for input like "aaa...aaaaz" the engine can get stuck trying to split the string into sub-matches.

That is, in the original case, the input "aaaz" had valid matches against `[rA-Z0-9a-f]+` up to "z" of:

aaa
aa…