fix(api): sync RRsets from pdns after dynamic update

This commit was tested manually.  I did not write a test for it because
the dynamic update mechanism will very soon be replaced by one based on
the RRset model.  The issue will then disappear.

api/desecapi/pdns.py

@@ -210,6 +210,9 @@ def set_dyn_records(domain):
         ]
     })
 
+    # Don't forget to import the updated RRsets
+    domain.sync_from_pdns()
+
     notify_zone(domain)