Steps to replicate the issue (include links if applicable):

• Edit a Scribunto script with CodeMirror on a WMF Wiki (in my case, enwiki)
• Reference mw.wikibase in the Lua code

What happens?:

• The Luacheck linter produces an info message "Accessing an undefined field of a global variable"

What should have happened instead?:

• wikibase, if loaded, should be recognized as part of the mw library, the same standard scribunto libraries such as ustring and html are

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

Not sure if this would require T394964 to be resolved first, or if there is another way of implementing this only on wikis where wikibase is enabled.