Eg. `workflow1` and `workflow2` both call `composite/action`:
.github/workflows/workflow1.yml
.github/workflows/workflow2.yml
.github/actions/composite/action.yml
The only missing bit in that is a bit more support in a composite action: `if` and a few other keywords. Also, it's a bit annoying to access private across across repos.
Which brings me the second comment... this is proof the docs suck. I have looked and looked for any evidence that this exact scenario was possible. There are no examples or documentation of this feature anywhere that I could find.
For a lot of Github Actions, I actually follow the Github Roadmap through to implementation as the PRs actually have good examples in them… https://github.com/github/roadmap/projects/1
This is all non-Enterprise, private repos, no clue in GHEC/S.