dist: do not distribute CI.md

[vszakats]

CI.md slipped into the 8.15.0, 8.16.0 tarballs by accident.
Remove it again and update the checker exception.

Follow-up to fa3f889 #17463

[bagder]

The way this is worded right now, it sounds like we remove a file from the tarball. In reality it just removes a path from a list that identifies a non-existing file since it was moved from there previously.

[vszakats]

This patch also removes CI.md from the tarball. CI.md wasn't part of it before
8.15.0. I assume this was by intent, because no CI-related file is distributed. Then,
while moving test .md files to their new location, CI.md got into the tarball. My
understanding is that this may have been unintented. Is this incorrect? (The exception
list needs to be updated either way.)

(I adjusted the title and text to better tell this.)

[bagder]

Aha. Yeah, since nothing CI related is included anyway I figure maybe the docs doesn't belong there. I don't feel strongly either way.