More precise return type for mysqli_fetch_all()

[oxan]

mysqli_fetch_all() and mysqli_result::fetch_all() returns a sequentially indexed array (list) of arrays, so convert its return type from array to list<array>.

The fullly specified return type for these functions is a bit more complicated, as it depends on the $mode parameter:

• If it's MYSQLI_ASSOC, it's a list of associative arrays, i.e. list<array<string, string|int|float|null>>.
• If it's MYSQLI_NUM, it's a list of lists, i.e. list<list<array|int|float|null>>.
• If it's MYSQLI_BOTH, it's a list of enumerated and associative arrays, i.e. list<array<string|int, string|int|float|null>>.

We could specify the return type as list<array<string|int, string|int|float|null>> to catch all these cases, but I'm not sure that'd be very helpful, as it might force users to deal with types in the union that will never happen in their case. The mysqli_fetch_array() and mysqli_result::fetch_array() functions that share the same polymorphic behaviour are also typehinted as just array.

I think the CI failure is unrelated.