let rerunning transcripts in CI be independent of yaml changes

[aryairani]

Currently, transcripts gets rerun if stack.yaml has changed. This was intentional because changing stack.yaml can affect how unison is built, and thus whether it works correctly.

However, it's incredibly slow to wait for when you're testing out unrelated parts of the YAML. We could change CI to only run transcripts if some .hs or .md changes, and not when the YAML alone changes.