* Fix pagination sort merge with prefixed default order

When sortableFields uses unprefixed field names (e.g., 'modified')
but the default order configuration uses prefixed names (e.g.,
'Articles.modified' => 'DESC'), the sort toggle would not work
correctly. The merge logic would add duplicate entries because
it didn't recognize that 'modified' and 'Articles.modified'
refer to the same field.

This fix normalizes field names during the merge by checking if
a prefixed field from the default order matches an unprefixed
field already present in the resolved order array.

Refs #17954

* Use assertSame instead of assertEquals for scalar values