Bump net-imap from 0.4.17 to 0.4.19

Bumps [net-imap](https://github.com/ruby/net-imap) from 0.4.17 to 0.4.19.
- [Release notes](https://github.com/ruby/net-imap/releases)
- [Commits](https://github.com/ruby/net-imap/compare/v0.4.17...v0.4.19

)

---
updated-dependencies:
- dependency-name: net-imap
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>