While this change is not 100% required now, it's good habit
and we are checking for it since Moodle 4.4.
All the changes in this commit have been applied automatically
using the moodle.PHPUnit.TestReturnType sniff and are, exclusively
adding the ": void" return types when missing.
This was detected when working in the renaming of test names:
- Fix file name, it was incorrectly named .test.php, now _test.php.
- Add namespace and rename testcase name to match file name.
- Fix php80 deprecation message about optional and required params
order.