Issue #23731: Implement PEP 488.

The concept of .pyo files no longer exists. Now .pyc files have an
optional `opt-` tag which specifies if any extra optimizations beyond
the peepholer were applied.
diff --git a/Lib/test/test_zipimport.py b/Lib/test/test_zipimport.py
index 0a83841..a97a778 100644
--- a/Lib/test/test_zipimport.py
+++ b/Lib/test/test_zipimport.py
@@ -51,7 +51,7 @@
 TEMP_ZIP = os.path.abspath("junk95142.zip")
 
 pyc_file = importlib.util.cache_from_source(TESTMOD + '.py')
-pyc_ext = ('.pyc' if __debug__ else '.pyo')
+pyc_ext = '.pyc'
 
 
 class ImportHooksBaseTestCase(unittest.TestCase):