Fix #20195: wrong reference in session settings documentation.

docs/ref/settings.txt

@@ -2372,7 +2372,7 @@ SESSION_EXPIRE_AT_BROWSER_CLOSE
 Default: ``False``
 
 Whether to expire the session when the user closes his or her browser. See
-"Browser-length sessions vs. persistent sessions" above.
+:ref:`browser-length-vs-persistent-sessions`.
 
 .. setting:: SESSION_FILE_PATH
 

docs/topics/http/sessions.txt

@@ -453,6 +453,8 @@ session cookie is sent.
 .. versionchanged:: 1.5
   The session is not saved if the response's status code is 500.
 
+.. _browser-length-vs-persistent-sessions:
+
 Browser-length sessions vs. persistent sessions
 ===============================================