add None return type to close() in viam_client (#963)

Author: eclair4151

src/viam/app/viam_client.py

@@ -206,7 +206,7 @@ async def main():
         """
         return ProvisioningClient(self._channel, self._metadata)
 
-    def close(self):
+    def close(self) -> None:
         """Close opened channels used for the various service stubs initialized."""
         if self._closed:
             LOGGER.debug("ViamClient is already closed.")