Add comment to test.

This documents the understanding between the engineers behind cl/570839777.

See also: cl/599883612

PiperOrigin-RevId: 599906511

clif/testing/python/std_containers_copy_move_test.py

@@ -23,6 +23,10 @@
 if tm.__pyclif_codegen_mode__ == "pybind11":
   ENV_IX += 2
 
+# NOTE: The tests here are known to be hyper-sensitive.
+#       It is expected that they will need to be adjusted or made more
+#       permissive (similar to e.g. return_value_policy_test.py).
+
 
 class StdContainersCopyMoveTestCase(parameterized.TestCase):