bug #45531 [Serializer] Fix passing null to str_contains() (Erwin Dirks)

This PR was merged into the 4.4 branch.

Discussion
----------

[Serializer] Fix passing null to str_contains()

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

In PHP 8.1 `null` isn't allowed so the check `str_contains` will fail because `$format` can be `null`

Commits
-------

da7d8c0 [Serializer] Fix passing null to str_contains()

src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php

@@ -472,7 +472,7 @@ private function validateAndDenormalize(string $currentClass, string $attribute,
             // PHP's json_decode automatically converts Numbers without a decimal part to integers.
             // To circumvent this behavior, integers are converted to floats when denormalizing JSON based formats and when
             // a float is expected.
-            if (Type::BUILTIN_TYPE_FLOAT === $builtinType && \is_int($data) && str_contains($format, JsonEncoder::FORMAT)) {
+            if (Type::BUILTIN_TYPE_FLOAT === $builtinType && \is_int($data) && null !== $format && str_contains($format, JsonEncoder::FORMAT)) {
                 return (float) $data;
             }