revert: remove overloaded $responseContentType

Author: ricklambrechts

src/OpenIDConnectClient.php

@@ -21,6 +21,11 @@ class OpenIDConnectClient extends \Jumbojett\OpenIDConnectClient
     protected ?JweDecryptInterface $jweDecrypter;
     protected ?OpenIDConfiguration $openIDConfiguration;
 
+    /**
+     * @var string|null Content type from the server
+     */
+    private ?string $responseContentType;
+
     public function __construct(
         ?string $providerUrl = null,
         ?string $clientId = null,