Symfony version(s) affected: Master-Branch

Description
There's an undefined variable in the PSR6 simple cache.

How to reproduce
I'm afraid, but I don't know where that would cause a problem, I've just noticed it when I was reading the code.

Possible Solution
Rename $value to $values.

Additional context
https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Cache/Simple/Psr6Cache.php#L157