Previously, when formatting commit messages, anything
that looked like SHA1 hashes was turned into a link
using regex. This meant that certain phrases or numbers
such as `777777` or `deadbeef` could be recognized as a commit
even if the repository has no commit with those hashes.
This change will make it so that anything that looks
like a SHA1 hash using regex will then also be checked
to ensure that there is a commit in the repository
with that hash before making a link.
Signed-off-by: Gary Kim <gary@garykim.dev>