Bump com.icegreen:greenmail from 2.1.0-alpha-3 to 2.1.0-alpha-4 (#8910)

Bumps [com.icegreen:greenmail](https://github.com/greenmail-mail-test/greenmail) from 2.1.0-alpha-3 to 2.1.0-alpha-4.
- [Release notes](https://github.com/greenmail-mail-test/greenmail/releases)
- [Commits](https://github.com/greenmail-mail-test/greenmail/compare/release-2.1.0-alpha-3...release-2.1.0-alpha-4)

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

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build.gradle

@@ -68,7 +68,7 @@ ext {
     derbyVersion = '10.16.1.1'
     ftpServerVersion = '1.2.0'
     graalvmVersion = '23.0.2'
-    greenmailVersion = '2.1.0-alpha-3'
+    greenmailVersion = '2.1.0-alpha-4'
     groovyVersion = '4.0.16'
     hamcrestVersion = '2.2'
     hazelcastVersion = '5.3.6'