[BUGFIX] Adjust return value in DeprecatingRequestWrapper

With #100567, the return type of the getPageArguments()
method in RequestWrapper and DeprecatingRequestWrapper
was changed to PageArguments, while the actual return value
was only adjusted in the RequestWrapper.

This is now also done in DeprecatingRequestWrapper.

Resolves: #100599
Related: #100567
Releases: main
Change-Id: I678451ccc31b7e3b72ab03bfb6b7ce1c0ba05138
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78642
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>

typo3/sysext/core/Classes/ExpressionLanguage/DeprecatingRequestWrapper.php

@@ -135,6 +135,6 @@ public function getPageArguments(): ?PageArguments
             ' based on the backend user object.',
             E_USER_DEPRECATED
         );
-        return $this->request->getAttribute('routing');
+        return ($routing = $this->request->getAttribute('routing')) instanceof PageArguments ? $routing : null;
     }
 }