Add compatibility with PHP 8.1 (#559)

Author: Jean85

.github/workflows/tests.yaml

@@ -18,6 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         php:
+          - '8.1'
           - '8.0'
           - '7.4'
           - '7.3'

tests/End2End/App/Controller/MainController.php

@@ -41,7 +41,7 @@ public function exception(): Response
 
     public function fatal(): Response
     {
-        $foo = eval("return new class() implements \Serializable {};");
+        $foo = eval("return new class() implements \JsonSerializable {};");
 
         return new Response('This response should not happen: ' . json_encode($foo));
     }

tests/End2End/End2EndTest.php

@@ -151,7 +151,7 @@ public function testGetFatal(): void
             $this->assertStringNotContainsString('not happen', $response->getContent() ?: '');
         } catch (\RuntimeException $exception) {
             $this->assertStringContainsStringIgnoringCase('error', $exception->getMessage());
-            $this->assertStringContainsStringIgnoringCase('contains 2 abstract methods', $exception->getMessage());
+            $this->assertStringContainsStringIgnoringCase('contains 1 abstract method', $exception->getMessage());
             $this->assertStringContainsStringIgnoringCase('MainController.php', $exception->getMessage());
             $this->assertStringContainsStringIgnoringCase('eval()\'d code on line', $exception->getMessage());
         }