Correct the name of SpatialMaterial for 3.x (#5477)

StandardMaterial3D should be SpatialMaterial on 3.x.

tutorials/shaders/your_first_shader/your_first_3d_shader.rst

@@ -5,7 +5,7 @@ Your first 3D shader
 
 You have decided to start writing your own custom Spatial shader. Maybe you saw
 a cool trick online that was done with shaders, or you have found that the
-:ref:`StandardMaterial3D <class_SpatialMaterial>` isn't quite meeting your
+:ref:`SpatialMaterial <class_SpatialMaterial>` isn't quite meeting your
 needs. Either way, you have decided to write your own and now you need figure
 out where to start.
 

tutorials/shaders/your_first_shader/your_second_3d_shader.rst

@@ -154,7 +154,7 @@ when you are looking at the surface head-on or at a glancing angle.
   float fresnel = sqrt(1.0 - dot(NORMAL, VIEW));
 
 And mix it into both ``ROUGHNESS`` and ``ALBEDO``. This is the benefit of
-ShaderMaterials over StandardMaterial3Ds. With StandardMaterial3D, we could set
+ShaderMaterials over SpatialMaterials. With SpatialMaterial, we could set
 these properties with a texture, or to a flat number. But with shaders we can
 set them based on any mathematical function that we can dream up.