`SlevomatCodingStandard.Functions.RequireMultiLineCall` incorrectly detects line length

[roslov]

Slevomat version: 8.25.0

Sniff: SlevomatCodingStandard.Functions.RequireMultiLineCall

There is a line in a legacy code:

        return !preg_match("/$regex/", (string) $value) ? "недопустимый формат, поле '$name'" : null;

The real line length is 101 chars.

But the sniff calculates it as 123.

Probably, we need to replace strlen with mb_strlen.