[management] Give the dns-config fixture the final newline the repo asks for

.editorconfig sets insert_final_newline for the repository and both golden files
in this case already end with one; nmdata.json never did. Noticed while editing
the file for the destination fixture, so fixed here rather than left for the
next person to trip over.

management/internals/controllers/network_map/nmaptest/testdata/cases/dns-config/nmdata.json

@@ -71,4 +71,4 @@
       }
     }
   ]
-}
+}