v8.1.0

• Add ie St Brigid's Day, the first Monday in February or 1 February when that day is a Friday, a public holiday from 2023, for definitions issue-348
• Restore sk Deň Ústavy Slovenskej republiky and Deň boja za slobodu a demokraciu, which were removed entirely in 5.9.0 despite remaining state holidays in Slovak law
• Mark sk Deň Ústavy Slovenskej republiky as informal from 2024 and Deň boja za slobodu a demokraciu as informal from 2025, the years each stopped being a day of rest, for definitions pull-288 (thanks to https://github.com/lucialopuchova)
• Clarify that informal also covers holidays that remain in law but are ordinary working days
• Add us_ut Juneteenth observance rule, observed on June 19 when that is a Monday, the preceding Monday when June 19 is Tuesday through Friday, and the following Monday when it is a weekend, for definitions pull-290 (thanks to https://github.com/philipwritescode)
• Allow region as a custom method argument, matching what doc/SYNTAX.md has always documented