Merge 2.0.x into 2.1.x

AssertEmptyIsDiscouragedRule: use unique error identifier

Author: staabm

src/Rules/PHPUnit/AssertEmptyIsDiscouragedRule.php

@@ -45,7 +45,7 @@ public function processNode(Node $node, Scope $scope): array
 
 		return [
 			RuleErrorBuilder::message(sprintf('%s() is not allowed. Use more strict assertion.', $node->name->toString()))
-				->identifier('empty.notAllowed')
+				->identifier('phpunit.assertEmpty')
 				->build(),
 		];
 	}