Update some www.unicode.org URLs to use HTTPS. (GH-18912)

diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index 8636f2b..2839889 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -1752,7 +1752,7 @@
         # Issue #8271: during the decoding of an invalid UTF-8 byte sequence,
         # only the start byte and the continuation byte(s) are now considered
         # invalid, instead of the number of bytes specified by the start byte.
-        # See http://www.unicode.org/versions/Unicode5.2.0/ch03.pdf (page 95,
+        # See https://www.unicode.org/versions/Unicode5.2.0/ch03.pdf (page 95,
         # table 3-8, Row 2) for more information about the algorithm used.
         FFFD = '\ufffd'
         sequences = [