Give backup page more time to render when querying

Just to be safe that we don't run into our request timeout during table
rendering etc. if the query already took a long time.

CMK-21529

Change-Id: Ia3d5fd6e8a0026ae955e403495b4d657377fa1e0

cmk/gui/backup/handler.py

@@ -1095,7 +1095,7 @@ def backups(self) -> _Backups:
         time0 = time.time()
         for ident, info in self.target.list_backups():
             backups[ident] = info
-            if time.time() - time0 > request.request_timeout - 10:
+            if time.time() - time0 > request.request_timeout - 20:
                 return _Backups(backups, timed_out=True)
         return _Backups(backups, timed_out=False)