pythongh-100600: Fix "coroutine was never awaited" warning in test_coroutines (python#100601)

Author: sobolevn

Lib/test/test_coroutines.py

@@ -2214,6 +2214,7 @@ async def f():
         gen = f()
         with self.assertWarns(RuntimeWarning):
             gen.cr_frame.clear()
+        gen.close()
 
     def test_stack_in_coroutine_throw(self):
         # Regression test for https://github.com/python/cpython/issues/93592