bug #25502 Fixing wrong class_exists on interface (weaverryan)

This PR was merged into the 3.4 branch.

Discussion
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Fixing wrong class_exists on interface

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | symfony/symfony-docs#8873 already does not mention changing anything in the config

This was a bug introduced in #25151 on the 3.4 branch. It's... pretty self-explanatory I hope :).

Cheers!

Commits
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be75bd994b Fixing wrong class_exists on interface

Author: fabpot

DependencyInjection/Configuration.php

@@ -143,7 +143,7 @@ private function addCsrfSection(ArrayNodeDefinition $rootNode)
         $rootNode
             ->children()
                 ->arrayNode('csrf_protection')
-                    ->{!class_exists(FullStack::class) && class_exists(CsrfTokenManagerInterface::class) ? 'canBeDisabled' : 'canBeEnabled'}()
+                    ->{!class_exists(FullStack::class) && interface_exists(CsrfTokenManagerInterface::class) ? 'canBeDisabled' : 'canBeEnabled'}()
                 ->end()
             ->end()
         ;