XKRX: Add extra holiday on 2023-10-02

[philiptromans]

XKRX: Added an extra temporary holiday for 2023-10-02. Exchange press release here.

Workflow to modify an existing Exchange Calendar

• Modify calendar class as required.
• Modify the test resources file (e.g tests/resources/{Exchange MIC}.csv), either manually or by executing python etc/make_exchange_calendar_test_csv.py {Exchange MIC}.
• Check if any of the fixtures in tests/test_{Exchange MIC}_calendar.py need updating to reflect your changes.
• Add references to any new/modified holidays in exchange_calendars/exchange_calendar_{Exchange MIC}.py.

[philiptromans]

Looks like CI is a bit broken.

[philiptromans]

I've added 83e9b05 which fixes CI. It should probably be in a separate PR though, so feel free to cherry pick if you want.