MNT: Use np.broadcast_shapes in interpolate_1d

We can rely on this with numpy >=1.20.

src/metpy/interpolate/one_dimension.py

@@ -107,8 +107,7 @@ def interpolate_1d(x, xp, *args, axis=0, fill_value=np.nan, return_list_always=F
     sort_x = np.argsort(x)
 
     # The shape after all arrays are broadcast to each other
-    # Can't use broadcast_shapes until numpy >=1.20 is our minimum
-    final_shape = np.broadcast(xp, *args).shape
+    final_shape = np.broadcast_shapes(xp.shape, *(a.shape for a in args))
 
     # indices for sorting
     sorter = broadcast_indices(sort_args, final_shape, axis)