[PHP] Date isn't correctly formatted

[a4blue]

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

swagger-api/swagger-codegen#6533
swagger-api/swagger-codegen#6474
swagger-api/swagger-codegen#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);