gh-102388: Add windows_31j to aliases for cp932 codec (#102389)

The charset name "Windows-31J" is registered in the IANA Charset Registry[1]
and is implemented in Python as the cp932 codec.

[1] https://www.iana.org/assignments/charset-reg/windows-31J

Signed-off-by: Masayuki Moriyama <masayuki.moriyama@miraclelinux.com>