[PHP] Date isn't correctly formatted

Description

Date is not correctly formatted from a DateTime Object in a generated PHP-Client
Expected was 'Y-m-d' instead 'Y-m-d\TH:i:sP' was generated

Swagger-codegen version

• 3.0.24
• git commit 912afd4052f5bb37064ba9e604e2ab1027eb83cf (swagger-codegen)

Swagger declaration file content or url

https://gist.github.com/a4blue/db06f076317ac6150a65b682e971039b

Command line used for generation

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i ../test.yml -l php -o ../test_api

Steps to reproduce

<?php
include_once "vendor/autoload.php";

$model = new \Swagger\Client\Model\Model();
$model->setSampleDate(new DateTime());
var_dump((string)$model);

Related issues/PRs

https://github.com/swagger-api/swagger-codegen/issues/6533
https://github.com/swagger-api/swagger-codegen/issues/6474
https://github.com/swagger-api/swagger-codegen/issues/5607

Suggest a fix/enhancement

In lib/ObjectSerializer.php:
Line 74

- $values[$data::attributeMap()[$property]] = self::sanitizeForSerialization($value, $swaggerType, $formats[$property]);
+ $values[$data::attributeMap()[$property]] = self::sanitizeForSerialization($value, $formats[$property], $swaggerType);

Start at lib/ObjectSerializer.php line 74 and reproduce the generated PHP client with the provided Swagger declaration and DateTime example. Check the serialization call's handling of the date format, then verify that casting the model produces the expected 'Y-m-d' value instead of 'Y-m-d\TH:i:sP'.