Add check for _PythonActorMeshAdapter and _PythonActorMeshRefAdapter (meta-pytorch#777)

Summary:
Pull Request resolved: meta-pytorch#777

Add 2 more checks so I can feel warm and fuzzy.

Reviewed By: moonli

Differential Revision: D79732646

fbshipit-source-id: b48a44ce7aefb2dade85c55b423e180fedf0d352

Author: pzhan9

python/monarch/_src/actor/actor_mesh.py

@@ -226,6 +226,10 @@ class _PythonActorMeshAdapter(ActorMeshProtocol):
     """
 
     def __init__(self, inner: PythonActorMesh, proc_mesh: "ProcMesh") -> None:
+        if _use_standin_mesh():
+            raise ValueError(
+                "_PythonActorMeshAdapter should only be used when USE_STANDIN_ACTOR_MESH is not set"
+            )
         self._inner = inner
         self._proc_mesh = proc_mesh
 
@@ -275,6 +279,10 @@ def __init__(
         inner: PythonActorMeshRef,
         proc_mesh: "Optional[ProcMesh]",
     ) -> None:
+        if _use_standin_mesh():
+            raise ValueError(
+                "_PythonActorMeshRefAdapter should only be used when USE_STANDIN_ACTOR_MESH is not set"
+            )
         self._inner = inner
         self._proc_mesh = proc_mesh