Update Ireland holidays

[KJhellico]

Proposed change

Update Ireland holidays:

• update/add some holidays' years of appearance
• remove observed holidays (since the exact day of observed holidays is not established by law)

Closes #1652.

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/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

[coveralls]

Pull Request Test Coverage Report for Build 7848523664

Warning: This coverage report may be inaccurate.

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A quick fix for this PR: rebase it; your next report should be accurate.

• 0 of 17 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 7793210723:	0.0%
Covered Lines:	10506
Relevant Lines:	10506

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💛 - Coveralls

[arkid15r]

LGTM

[sonarcloud]

Quality Gate passed

Issues
7 New issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[arkid15r]

🇮🇪 LGTM