Proposed change

I tried to better utilise the now centralised test setups implemented in #2881 by switching to assert{variant}HolidayDatesInYear and assert{variant}HolidaysInYear test methods to avoid duplicate test setups.

While not as blazingly fast as before that PR was implemented, which was ~55-70s (as we've yet to port all remaining countries' tests to the new system - see #3065 ), this should help us a bit.

### Pre-Optimized
110.33s 
111.99s
104.15s
Avg Time: 108.82s

### Post-`InYear` Tests Implementation
99.01s
92.54s
96.70s
Avg Time: 96.08s

Note that this still excludes cases where we did year-specific checks for multiple categories at the same time.

Type of change

• New country/market holidays support (thank you!)
• Supported country/market holidays update (calendar discrepancy fix, localization)
• Existing code/documentation/test/process quality improvement (best practice, cleanup, refactoring, optimization)
• Dependency update (version deprecation/pin/upgrade)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (a code change causing existing functionality to break)
• New feature (new holidays functionality in general)

Checklist

• I've read and followed the contributing guidelines.
• I've run make check locally; all checks and tests passed.