Fix PHPStan issues for src/FosRestBundle/FlattenExceptionHandler.php

All bundled in one commit to not flood the history, all of these should
be trivial on itself but help PHPStan to detect more issues.

Author: vmcj

phpstan-baseline.neon

@@ -365,16 +365,6 @@ parameters:
 			count: 1
 			path: webapp/src/Entity/User.php
 
-		-
-			message: "#^Method App\\\\FosRestBundle\\\\FlattenExceptionHandler\\:\\:convertToArray\\(\\) return type has no value type specified in iterable type array\\.$#"
-			count: 1
-			path: webapp/src/FosRestBundle/FlattenExceptionHandler.php
-
-		-
-			message: "#^Method App\\\\FosRestBundle\\\\FlattenExceptionHandler\\:\\:getSubscribingMethods\\(\\) return type has no value type specified in iterable type array\\.$#"
-			count: 1
-			path: webapp/src/FosRestBundle/FlattenExceptionHandler.php
-
 		-
 			message: "#^Method App\\\\FosRestBundle\\\\FlattenExceptionHandler\\:\\:serializeToJson\\(\\) has parameter \\$type with no value type specified in iterable type array\\.$#"
 			count: 1

webapp/src/FosRestBundle/FlattenExceptionHandler.php

@@ -22,6 +22,9 @@ public function __construct(
         private readonly bool $debug
     ) {}
 
+    /**
+     * @return array<array{direction: int, format: string, type: string, method: string}>
+     */
     public static function getSubscribingMethods(): array
     {
         return [
@@ -44,6 +47,9 @@ public function serializeToJson(
             $type);
     }
 
+    /**
+     * @return array{code: int, message: string}
+     */
     private function convertToArray(
         FlattenException $exception,
         Context $context