[php-symfony] Update model_variables.mustache

[Starkmann]

Recursive validate non primitive objects

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[wing328]

cc @jebentier (2017/07), @dkarlovi (2017/07), @mandrean (2017/08), @jfastnacht (2017/09), @ackintosh (2017/09) ❤️, @ybelenko (2018/07), @renepardon (2018/12)

[ybelenko]

Did you update samples? Weird, no changes in samples at all.

[wing328]

Tested locally by making category a required property, I got the following (partial result):

     /**
-     * @var OpenAPI\Server\Model\Category|null
+     * @var OpenAPI\Server\Model\Category
      * @SerializedName("category")
+     * @Assert\NotNull()
+     * @Assert\Valid()
      * @Assert\Type("OpenAPI\Server\Model\Category")
      * @Type("OpenAPI\Server\Model\Category")
      */

[wing328]

#11810 has been merged to support Symfony 6. Please give it a try and let us know if you've any feedback or question.