[3.9] bpo-25130: Add calls of gc.collect() in tests to support PyPy (GH-28005). (GH-28028)

(cherry picked from commit 2a8127cafe)

Lib/test/test_asyncgen.py

@@ -3,6 +3,7 @@
 import unittest
 
 from test.support import import_module
+from test.support import gc_collect
 asyncio = import_module("asyncio")
 
 
@@ -659,6 +660,7 @@ async def run():
             await g.__anext__()
             await g.__anext__()
             del g
+            gc_collect()  # For PyPy or other GCs.
 
             await asyncio.sleep(0.1)