minor #11723 Update impersonating_user.rst (acrnogor)

This PR was submitted for the 4.3 branch but it was merged into the 4.2 branch instead (closes #11723).

Discussion
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Update impersonating_user.rst

- request->getSession method call was missing brackets - fixed

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Commits
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685757b Update impersonating_user.rst

Author: javiereguiluz

security/impersonating_user.rst

@@ -324,7 +324,7 @@ you switch users, add an event subscriber on this event::
         {
             $request = $event->getRequest();
 
-            if ($request->hasSession() && ($session = $request->getSession)) {
+            if ($request->hasSession() && ($session = $request->getSession())) {
                 $session->set(
                     '_locale',
                     // assuming your User has some getLocale() method