ci: doc-publish: Publish API coverage docs only when available

The API coverage documentation support was (relatively) recently introduced
in bad87f1684e7fe8be11a39290d688d9585549184 and is not available in older
release branches.

Since doc-publish workflows always run in the default (main) branch
context, it is necessary to make the API coverage documentation handling
optional for the workflow runs that are triggered from older release
branches.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
2 files changed