This PR was submitted for the 4.3 branch but it was merged into the 4.4 branch instead.Discussion----------[DI] Unknown env prefix not recognized as such| Q             | A| ------------- | ---| Branch?       | 4.3| Bug fix?      | yes| New feature?  | no| Deprecations? | no| Tickets       | Fix #... <!-- prefix each issue number with "Fix #", if any -->| License       | MIT| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->This is a failing test to illustrate the difference between real and fake env vars when using an unknown prefix, followed by the `default` prefix.```%env(unknown:default::REAL)%// Unsupported env var prefix "unknown".%env(unknown:default::FAKE)%// null```For `default::FAKE` we get `null` athttps://github.com/symfony/symfony/blob/38b9a27976d36c4ffbfeb9e666319d77ffc8b3c0/src/Symfony/Component/DependencyInjection/EnvVarProcessor.php#L103which is then preserved athttps://github.com/symfony/symfony/blob/38b9a27976d36c4ffbfeb9e666319d77ffc8b3c0/src/Symfony/Component/DependencyInjection/EnvVarProcessor.php#L123need inspiration for a patch still :)Commits-------550819a [DI] Unknown env prefix not regornized as such