XTKS: Add 2024 Vernal and Autumnal equinoxes

According to
https://www.jpx.co.jp/english/corporate/about-jpx/calendar/index.html,
https://www.timeanddate.com/holidays/japan/spring-equinox, and
https://www.timeanddate.com/holidays/japan/autumn-equinox,
in 2024 Vernal Equinox will happen on Mar. 20 (Wed.), and Autumnal
Equinox will happen on Sep. 22 (Sun.)., observed on Sep. 23 (Mon.)

exchange_calendars/xtks_holidays.py

@@ -99,6 +99,7 @@ def sunday_to_wednesday(dt):
     Timestamp("2021-03-20"),
     Timestamp("2022-03-21"),
     Timestamp("2023-03-21"),
+    Timestamp("2024-03-20"),
 ]
 
 # The Golden Week holidays (late April - early May) are listed in reverse
@@ -263,6 +264,8 @@ def sunday_to_wednesday(dt):
     Timestamp("2021-09-23"),
     Timestamp("2022-09-23"),
     Timestamp("2023-09-23"),
+    Timestamp("2024-09-22"),
+    Timestamp("2024-09-23"),  # observed
 ]
 
 # If the Autumnal Equinox falls on a Wednesday, the Tuesday before