Fix CsrfProtection callable and move it to array callback format (#213)

* Fix CsrfProtection callable and move it to array callback format

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Co-authored-by: Marko Ivančić <marko.ivancic@srce.hr>

src/Forms/Controls/CsrfProtection.php

@@ -24,7 +24,7 @@
 
 class CsrfProtection extends BaseCsrfProtection
 {
-    final public const PROTECTION = 'SimpleSAML\Module\oidc\Form\Controls\CsrfProtection::validateCsrf';
+    final public const PROTECTION = [\SimpleSAML\Module\oidc\Forms\Controls\CsrfProtection::class, 'validateCsrf'];
 
     protected Session $sspSession;