Tests: Give canonical test fixtures for paginated content more descriptive names.

Follow-up to [47727].

See #28081, #40773, #45337.
Built from https://develop.svn.wordpress.org/trunk@47781


git-svn-id: https://core.svn.wordpress.org/trunk@47557 1a063a9b-81f0-0310-95a4-ce76da25c4cd