HEMCO submod update: Merge PR #274 (Use "stale" GitHub action)

This commit informs the GCClassic superproject about the following
commits that were pushed to the GitHub geoschem/geos-chem repository:

f3fae96 Merge PR #274 (Replace stalebot with "stale" GitHub action)

This PR replaces the obsolete GitHub stalebot with the newer
"stale" GitHub action.

Signed-off-by: Bob Yantosca <[email protected]>