With PHPUnit 9, tests without @covers tags are considered risky and emit
warnings. Not having @covers is bad practice anyway, so use
@coversNothing instead to make the intention clear, and re-enable the
phpcs rule.
Also rewrite an assertion in ResourcesTest that was bothering me.
Bug: T243600
Change-Id: I6dd683f93b6b2faed5f107be2ca7860602277fbc