wp_set_current_user() is type strict determing current user

[peterwilsoncc]

The wp_set_current_user() function returns early if the function is called with the current user ID to avoid the work of switching users when it's not required.

However, the function uses a type strict comparison when determining if the user ID is the same, so wp_set_current_user( (int) get_current_user_id() ) will return early, whereas wp_set_current_user( (string) get_current_user_id() ) will proceed through the set up of the new current user.

Introduced in r57882 for #60700.

This is a minor fix (tests and PR incoming) so I've put it on the 7.0 milestone.

Ensures the user switching does not occur when attempting to switch to the same user with the user ID cast to a string.

Trac ticket: https://core.trac.wordpress.org/ticket/64628

## Use of AI Tools

Nil.

[peterwilsoncc]

In 61633:

Users: Ensure switching to current user doesn't reinstantiate current user.

Prevent wp_set_current_user() from reinstantiating the current user when the user ID is passed as a string, eg wp_set_current_user( (string) get_current_user_id() ).

This restores the function's previous behaviour of returning early in the event the IDs loosely match.

Follow up to r57882.

Props westonruter, peterwilsoncc.
Fixes #64628.