This is a gem housekeeping release. No user-facing changes.

🏠 Housekeeping

• CI: Use newer Vagrant box to address timeout issues (#517) @mattbrictson
• Bump toolmantim/release-drafter from 5.23.0 to 5.24.0 (#515) @dependabot
• Fix CI failures by running Ruby <= 2.2 on older Ubuntu image (#516) @mattbrictson
• Bump actions/cache from 2 to 3 (#511) @dependabot
• Increase Vagrant boot timeout to accommodate slow GitHub Actions (#513) @mattbrictson
• Bump toolmantim/release-drafter from 5.22.0 to 5.23.0 (#510) @dependabot
• Upgrade macOS runner in CI since GitHub has retired 10.15 (#512) @mattbrictson

Full Changelog: https://github.com/capistrano/sshkit/compare/v1.21.4...v1.21.5