test(phpstan): Fix PHPstan check (#3467196)

.github/workflows/close-pull-requests.yml

@@ -13,4 +13,3 @@ jobs:
         comment: |
           Please open issues and pull requests on drupal.org: https://www.drupal.org/project/issues/graphql
           Auto-closing this pull request.
-

tests/src/Kernel/Framework/LoggerTest.php

@@ -52,8 +52,13 @@ GQL;
 
   /**
    * {@inheritdoc}
+   *
+   * @todo For some reason, PHPStan wants to see a type hint for the level here,
+   * which is not correct.
+   *
+   * @phpstan-ignore-next-line
    */
-  public function log($level, $message, array $context = []): void {
+  public function log($level, string|\Stringable $message, array $context = []): void {
     $this->loggerCalls[] = [
       'level' => $level,
       'message' => $message,