Bump com.icegreen:greenmail from 2.1.7 to 2.1.8

Bumps [com.icegreen:greenmail](https://github.com/greenmail-mail-test/greenmail) from 2.1.7 to 2.1.8.
- [Release notes](https://github.com/greenmail-mail-test/greenmail/releases)
- [Commits](https://github.com/greenmail-mail-test/greenmail/compare/release-2.1.7...release-2.1.8)

---
updated-dependencies:
- dependency-name: com.icegreen:greenmail
  dependency-version: 2.1.8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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