[css2] css2 draft "Suggest an edit" link is broken

[dholbert]

STR:

1. Visit https://drafts.csswg.org/css2/
2. Click the link for "Suggest an Edit for this Spec" / "GitHub Editor"

ACTUAL RESULTS:
It takes you to
https://github.com/w3c/csswg-drafts/blob/main/CSS2/Overview.bs
which is 404

EXPECTED RESULTS:
It probably should have linked to this URL with lowercase css:
https://github.com/w3c/csswg-drafts/blob/main/css2/Overview.bs

I suspect the issue (the reason we're ending up with uppercase) is because the bikeshed file has this line near the top:

Shortname: CSS2

I'd bet the expectation is that Shortname matches the directory name in the git repo, and in this case that's css2, not CSS2.