bpo-33988: Fix test_warnings using -W error (GH-7985)

Use DeprecationWarning instead of PendingDeprecationWarning.
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 7bbaa9f..d80e8d3 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -4145,7 +4145,7 @@
                 'ignore',
                 r'dist\(\) and linux_distribution\(\) '
                 'functions are deprecated .*',
-                PendingDeprecationWarning,
+                DeprecationWarning,
             )
             for name, func in plats.items():
                 plat = func()