Doomsday Algorithm: Fix leap year check (#12396)

* Fix leap year check

Replace `!=` in `(year % 400) != 0` (line 49) with `==`

Justification: Years that are divisible by 100 (centurian == 100) but not by 400 (year % 400 != 0) are skipped and NOT leap year.

* Update parentheses

Correct the parentheses to make clear the precedence of the conditional check

* Update other/doomsday.py

Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>

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Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>