bpo-32323: urllib.parse.urlsplit() must not lowercase() IPv6 scope value (#4867)

diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py
index 76086e5..58460f9 100644
--- a/Lib/urllib/parse.py
+++ b/Lib/urllib/parse.py
@@ -155,10 +155,12 @@
     def hostname(self):
         hostname = self._hostinfo[0]
         if not hostname:
-            hostname = None
-        elif hostname is not None:
-            hostname = hostname.lower()
-        return hostname
+            return None
+        # Scoped IPv6 address may have zone info, which must not be lowercased
+        # like http://[fe80::822a:a8ff:fe49:470c%tESt]:1234/keys
+        separator = '%' if isinstance(hostname, str) else b'%'
+        hostname, percent, zone = hostname.partition(separator)
+        return hostname.lower() + percent + zone
 
     @property
     def port(self):