Fix pyre errors

Summary:
attempt to fix
```
    [executorch/exir/backend/test/demos/rpc/executor_backend_partitioner.py:68:19] Undefined attribute [16]: `None` has no attribute `op`.
    [executorch/exir/backend/test/demos/rpc/executor_backend_partitioner.py:69:20] Undefined attribute [16]: `None` has no attribute `meta`.
    [executorch/exir/backend/test/test_backends_nested.py:200:20] Undefined attribute [16]: `None` has no attribute `meta`.
```

in D79768387

Differential Revision: D79828275

Author: izaitsevfb

exir/backend/test/demos/rpc/executor_backend_partitioner.py

@@ -65,7 +65,9 @@ def partition(self, edge_exported_program: ExportedProgram) -> PartitionResult:
                 partition_tags[delegation_tag] = self.delegation_spec
 
                 # Tag the delegate submodules
+                # pyre-ignore[16]: node.args[0] is checked above but Pyre can't infer it
                 if node.args[0].op == "get_attr":
+                    # pyre-ignore[16]: node.args[0] is checked above but Pyre can't infer it
                     node.args[0].meta["delegation_tag"] = delegation_tag
 
         return PartitionResult(

exir/backend/test/test_backends_nested.py

@@ -197,7 +197,9 @@ def _partition_graph_module(
                     and node.target is torch.ops.higher_order.cond
                 ):
                     # Tag the arguments that take in the submodules to cond
+                    # pyre-ignore[16]: node.args[1] is checked above but Pyre can't infer it
                     node.args[1].meta["delegation_tag"] = delegation_tag
+                    # pyre-ignore[16]: node.args[2] is checked above but Pyre can't infer it
                     node.args[2].meta["delegation_tag"] = delegation_tag
                 node.meta["delegation_tag"] = delegation_tag
                 partition_tags[delegation_tag] = self.delegation_spec