[4.0.x] Fixed #33338 -- Doc'd that never_cache() decorator set Expires header.

Backport of 669dcefc04 from main

AUTHORS

@@ -588,6 +588,7 @@ answer newbie questions, and generally made Django that much better:
     Marc Aymerich Gubern
     Marc Egli <frog32@me.com>
     Marcel Telka <marcel@telka.sk>
+    Marcelo Galigniana <marcelogaligniana@gmail.com>
     Marc Fargas <telenieko@telenieko.com>
     Marc Garcia <marc.garcia@accopensys.com>
     Marcin Wróbel

docs/ref/utils.txt

@@ -62,10 +62,14 @@ need to distinguish caches by the ``Accept-language`` header.
 
 .. function:: add_never_cache_headers(response)
 
+    Adds an ``Expires`` header to the current date/time.
+
     Adds a ``Cache-Control: max-age=0, no-cache, no-store, must-revalidate,
     private`` header to a response to indicate that a page should never be
     cached.
 
+    Each header is only added if it isn't already set.
+
 .. function:: patch_vary_headers(response, newheaders)
 
     Adds (or updates) the ``Vary`` header in the given ``HttpResponse`` object.

docs/topics/http/decorators.txt

@@ -118,10 +118,14 @@ client-side caching.
 
 .. function:: never_cache(view_func)
 
+    This decorator adds an ``Expires`` header to the current date/time.
+
     This decorator adds a ``Cache-Control: max-age=0, no-cache, no-store,
     must-revalidate, private`` header to a response to indicate that a page
     should never be cached.
 
+    Each header is only added if it isn't already set.
+
 .. module:: django.views.decorators.common
 
 Common