v6.1.0

• Introduce mc (Monaco) region (thanks to https://github.com/abenhamdine)
• Fix fr Pentecote Sunday to be an official public holiday (thanks to https://github.com/abenhamdine)
• Fix gb Cornwall holidays for holidays issue-160
• Fix us_ga April State Holiday for years post-2020 (thanks to https://github.com/joseph-carino)
• Add validation to ensure that all regions are represented in index.yaml
• Run downstream smoke tests instead of the full test suite on PR/push