Docs: fix invalid XML docs for three sniffs

[jrfnl]

Each of these three sniffs had a <code_comparison> block containing three <code> elements instead of two.

Discovered by validating the docs against the XSD schema created by the amazing @dingo-d. The XSD schema is now available in PHPCSDevTools 1.2.0 as discussed in #3585.

If you're interested, I could refresh (a variation of) PR #2872 to add XML doc validation against the schema to the GH Actions checks.