Use OESeeror instead of os.error (#16720)

Patch by Serhiy Storchaka.
diff --git a/Tools/scripts/untabify.py b/Tools/scripts/untabify.py
index 4b67c15..861c83c 100755
--- a/Tools/scripts/untabify.py
+++ b/Tools/scripts/untabify.py
@@ -39,11 +39,11 @@
     backup = filename + "~"
     try:
         os.unlink(backup)
-    except os.error:
+    except OSError:
         pass
     try:
         os.rename(filename, backup)
-    except os.error:
+    except OSError:
         pass
     with open(filename, "w", encoding=encoding) as f:
         f.write(newtext)