Add juneteenth as variable holiday
When Juneteenth is on weekends, an additional holiday is added on fridays or mondays according to https://www.timeanddate.com/holidays/us/juneteenth
Year Weekd Date Name
2021 Fr 18. Jun Juneteenth (substitute)
2021 Sa 19. Jun Juneteenth
2022 So 19. Jun Juneteenth
2022 Mo 20. Jun Juneteenth (substitute)
2023 Mo 19. Jun Juneteenth
2024 Mi 19. Jun Juneteenth
2025 Do 19. Jun Juneteenth
2026 Fr 19. Jun Juneteenth
2027 Fr 18. Jun Juneteenth (substitute)
2027 Sa 19. Jun Juneteenth
2028 Mo 19. Jun Juneteenth