Upgrade PHPUnit to 9.5

Summary:
The 9.3 phar doesn't seem to work under PHP 8.1.

Ref T1677

Test Plan: Run CI job for rNOTIF

Reviewers: DorianWinty

Reviewed By: DorianWinty

Maniphest Tasks: T1677

Differential Revision: https://devcentral.nasqueron.org/D2682