minor #15531 [Mercure] Invalid namespace and method name (zspine)

This PR was submitted for the 5.3 branch but it was merged into the 4.4 branch instead.

Discussion
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[Mercure] Invalid namespace and method name

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Commits
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500d301 Invalid namespace and method name

Author: OskarStark

mercure.rst

@@ -450,11 +450,11 @@ the ``HubInterface`` object::
     // src/Mercure/MyTokenProvider.php
     namespace App\Mercure;
 
-    use Symfony\Component\Mercure\JWT\TokenProviderInterface;
+    use Symfony\Component\Mercure\Jwt\TokenProviderInterface;
 
     final class MyTokenProvider implements TokenProviderInterface
     {
-        public function getToken(): string
+        public function getJwt(): string
         {
             return 'the-JWT';
         }