Update Cambodian holidays for 2024

[PPsyrius]

Proposed change

April 16, 2024 is in fact declared as part of extended "Khmer New Year" (Sangkranta) holidays as seen in here (Web Archive Copy).

This also updates the list of years when such holiday started on APR 14 (instead of the usual APR 13) as shown on its Wikipedia page.

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 python-holidays functionality in general)

Checklist

• I've followed the contributing guidelines
• I've run make pre-commit, it didn't generate any changes
• I've run make test, all tests passed locally

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (5c3250e) to head (548bbf6).
Report is 2 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev     #1936   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          186       186           
  Lines        11315     11316    +1     
  Branches      1789      1789           
=========================================
+ Hits         11315     11316    +1     

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