security/ruby-sshkit: update to 1.21.5

1.21.5 (2023-07-04)

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

Contributors

* @mattbrictson
* @dependabot

(taca)