Fix typo in Paths.valid docstring

Fix Paths.valid docstring

Author: faycalaa

src/sionna/rt/path_solvers/paths.py

@@ -216,7 +216,7 @@ def valid(self):
         """
         Flags indicating valid paths
 
-        :type: :py:class:`mi.TensorXb [num_rx, num_rx_ant, num_tx, num_tx_ant, num_paths]`
+        :type: :py:class:`mi.TensorXb [num_rx, num_rx_ant, num_tx, num_tx_ant, num_paths]  or [num_rx, num_tx, num_paths]`
         """
         return self._valid