Update tests/test_loop.py

Co-authored-by: Sviatoslav Sydorenko <[email protected]>

tests/test_loop.py

@@ -14,6 +14,7 @@
     platform.system() == "Windows", reason="the test is not valid for Windows"
 )
 async def test_subprocess_co(loop: Any) -> None:
+    assert PY_38 or threading.current_thread() is threading.main_thread()
     proc = await asyncio.create_subprocess_shell(
         "exit 0",
         stdin=asyncio.subprocess.DEVNULL,