Interesting idea! Even if Actions will follow a submodule though (I doubt it tbh, it happens before any actions run of course so we have no control over that) you can't point it 'at trunk' as far as I know, they're always at a specific commit.
(E.g. if you git submodule foreach git checkout master, your diff if you have one will be updating commit hashes, not -whatever +master. This is good for a lot of other reasons but doesn't help here.)
(E.g. if you git submodule foreach git checkout master, your diff if you have one will be updating commit hashes, not -whatever +master. This is good for a lot of other reasons but doesn't help here.)