Mark the 410 gone response for suspended accounts as cachable (mastod…

…on#10339)

This will help a great deal with mastodon#9377 when a caching reverse proxy is
configured.

app/controllers/concerns/account_controller_concern.rb

@@ -69,6 +69,10 @@ def check_account_approval
   end
 
   def check_account_suspension
-    gone if @account.suspended?
+    if @account.suspended?
+      skip_session!
+      expires_in(3.minutes, public: true)
+      gone
+    end
   end
 end