GitLab

Same reason as tools/, at the owner's direction: the check suites are internal
testing rather than part of the product.  They stay on the machines that run
them.  Nothing shipped depended on them, only comments naming a file.

The hook refuses checks/ now as well, checked by staging a file under it and
watching the commit be refused.  The gitignore note that said checks/ is
committed said so one line above the rule that made it true, and it is
corrected rather than deleted, because the trap it warns about is real: a
suite written into an ignored directory is left out of every commit and
nothing tells you.

The README's testing section documented how to run suites a clone will not
have.  It now says where they live and what ships instead.