[12.x] fix data_has empty check

[rodrigopedra]

Continuation of #57580

As noted by @decadence in their comment #57580 (comment)

This function returns false for valid 0 key or I'm missing something? For example:

$array = [1, 2, 3];

data_has($array, "0"); // wrong false

That is due to empty($target) evaluating to true if the $key is a string equal to '0'.

This PR:

• Fixes the test for an empty key
• Adds more assertions to the data_has test case

Thanks @decadence