asyncio.test_tasks: Fix test_env_var_debug to use correct asyncio module

Lib/test/test_asyncio/test_tasks.py

 """Tests for tasks.py."""
 
+import os
 import re
 import sys
 import types
@@ -1768,25 +1769,31 @@ class GatherTestsBase:
         self.assertEqual(fut.result(), [3, 1, exc, exc2])
 
     def test_env_var_debug(self):
+        aio_path = os.path.dirname(os.path.dirname(asyncio.__file__))
+
         code = '\n'.join((
             'import asyncio.coroutines',
             'print(asyncio.coroutines._DEBUG)'))
 
         # Test with -E to not fail if the unit test was run with
         # PYTHONASYNCIODEBUG set to a non-empty string
-        sts, stdout, stderr = assert_python_ok('-E', '-c', code)
+        sts, stdout, stderr = assert_python_ok('-E', '-c', code,
+                                               PYTHONPATH=aio_path)
         self.assertEqual(stdout.rstrip(), b'False')
 
         sts, stdout, stderr = assert_python_ok('-c', code,
-                                               PYTHONASYNCIODEBUG='')
+                                               PYTHONASYNCIODEBUG='',
+                                               PYTHONPATH=aio_path)
         self.assertEqual(stdout.rstrip(), b'False')
 
         sts, stdout, stderr = assert_python_ok('-c', code,
-                                               PYTHONASYNCIODEBUG='1')
+                                               PYTHONASYNCIODEBUG='1',
+                                               PYTHONPATH=aio_path)
         self.assertEqual(stdout.rstrip(), b'True')
 
         sts, stdout, stderr = assert_python_ok('-E', '-c', code,
-                                               PYTHONASYNCIODEBUG='1')
+                                               PYTHONASYNCIODEBUG='1',
+                                               PYTHONPATH=aio_path)
         self.assertEqual(stdout.rstrip(), b'False')