Update Vietnam holidays

[KJhellico]

Proposed change

Update Vietnam holidays:

• update Lunar New Year holidays calculation
• add substituted holidays

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 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

[sonarqubecloud]

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 (1f3170f) to head (b1aae72).
Report is 13 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev     #2049   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          190       190           
  Lines        11522     11537   +15     
  Branches      1798      1743   -55     
=========================================
+ Hits         11522     11537   +15     

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[PPsyrius]

LGTM 🇻🇳

[arkid15r]

Nicely done!