testSum failures under PHP 8.3

[NorthNick]

There are 4 testSum tests, each including the sum of ["a", true, false, null]. The implementation of Sum uses array_sum, which throws a warning when values cannot be converted to int or float under PHP 8.3 (manual page). This causes the test suite to fail, so these tests should be changed or dropped, or modified to expect a warning from PHP 8.3 onwards.

[rtheunissen]

I would like to match array semantics as much as possible, so I think that means the tests should change from 8.3 onwards.