Relax the UUID regex

Apparently PG does not validate against RFC 4122. The intent of the original
patch is just to protect against PG errors (which potentially breaks txns, etc)
because of bad user input, so we shouldn't try any harder than PG itself.

Closes #17931
adds another examle to the constants not missing gotcha [ci skip]

/cc @matthewd
passed a spell checker, not bad [ci skip]
Spelling fix [ci skip]
Merge pull request #18087 from georgemillo/patch-2

Spelling fix [ci skip]
Add docs for AS::TestCase::test_order

Document `test_order` and `test_order=` from `ActiveSupport::TestCase`.

[ci skip]