Merge branch '6.4' into 7.1

* 6.4:
  Make more data providers static
  fix merge
  Mutate remaining data providers to static ones

Tests/MessageTest.php

@@ -306,7 +306,7 @@ public function testEnsureValidity(array $headers, ?string $exceptionClass, ?str
         $m->ensureValidity();
     }
 
-    public function ensureValidityProvider()
+    public static function ensureValidityProvider(): array
     {
         return [
             'Valid address fields' => [