Attempted fix for PHPstan-issues

Author: tvdijen

src/Codebooks/MetadataPolicyOperatorsEnum.php

@@ -137,18 +137,26 @@ public function getSupportedParameterContainedValueTypes(): array
 
 
     /**
-     * @phpstan-ignore missingType.iterableValue (We can handle mixed type using array_diff)
+     * @param mixed $value   scalar or stringable object
+     * @param string[] $superset
      */
     public function isValueSubsetOf(mixed $value, array $superset): bool
     {
         $value = is_array($value) ? $value : [$value];
 
-        return array_diff($value, $superset) === [];
+        $cast = static fn(mixed $v): string|int|float|bool|null =>
+            is_object($v) && method_exists($v, '__toString') ? (string) $v : $v;
+
+        return array_diff(
+            array_map($cast, $value),
+            array_map($cast, $superset)
+        ) === [];
     }
 
 
     /**
-     * @phpstan-ignore missingType.iterableValue (We can handle mixed type using array_diff)
+     * @param string|int|float|bool|null|object $value   scalar or stringable object
+     * @param array<string|int|float|bool|null|object> $subset
      */
     public function isValueSupersetOf(mixed $value, array $subset): bool
     {