Reference base and head refs in commit message

[mosherc]

Anyone know of a way to reference the base_ref and head_ref in the commit message? Our normal commits that update with the base branch look like Merge 'main' into feature/name-of-head-branch and looks like base_ref and head_ref are blank in pushes to main (makes sense), so would love a way to reference those two when the action finds a branch that needs updating.