Point ReturnNullableTypeRectorPhp82Test to its own fixtures and config

It read the same Fixture directory with the default config, so FixturePhp82
and configured_rule_php82.php never ran, and both test classes wrote the
same temporary input files, which fails randomly when the chunks run in
parallel (hash_file on a file the other class just deleted).

Author: GErpeldinger

rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnNullableTypeRector/ReturnNullableTypeRectorPhp82Test.php

@@ -18,11 +18,11 @@ public function test(string $filePath): void
 
     public static function provideData(): Iterator
     {
-        return self::yieldFilesFromDirectory(__DIR__ . '/Fixture');
+        return self::yieldFilesFromDirectory(__DIR__ . '/FixturePhp82');
     }
 
     public function provideConfigFilePath(): string
     {
-        return __DIR__ . '/config/configured_rule.php';
+        return __DIR__ . '/config/configured_rule_php82.php';
     }
 }