Update greenmail.version to v1.6.15

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.icegreen:greenmail-junit5 (source)	1.6.0 -> 1.6.15
com.icegreen:greenmail (source)	1.6.0 -> 1.6.15
com.icegreen:greenmail-junit5 (source)	1.6.5 -> 1.6.15

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[!WARNING] Some dependencies could not be looked up. Check the Dependency Dashboard for more information.

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Release Notes

greenmail-mail-test/greenmail (com.icegreen:greenmail-junit5)

### [`v1.6.15`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.14...release-1.6.15) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.14...release-1.6.15) ### [`v1.6.14`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.13...release-1.6.14) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.13...release-1.6.14) ### [`v1.6.13`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.12...release-1.6.13) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.12...release-1.6.13) ### [`v1.6.12`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.11...release-1.6.12) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.11...release-1.6.12) ### [`v1.6.11`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.10...release-1.6.11) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.10...release-1.6.11) ### [`v1.6.10`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.9...release-1.6.10) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.9...release-1.6.10) ### [`v1.6.9`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.8...release-1.6.9) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.8...release-1.6.9) ### [`v1.6.8`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.7...release-1.6.8) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.7...release-1.6.8) ### [`v1.6.7`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.6...release-1.6.7) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.6...release-1.6.7) ### [`v1.6.6`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.5...release-1.6.6) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.5...release-1.6.6) ### [`v1.6.5`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.4...release-1.6.5) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.4...release-1.6.5) ### [`v1.6.4`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.3...release-1.6.4) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.3...release-1.6.4) ### [`v1.6.3`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.2...release-1.6.3) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.2...release-1.6.3) ### [`v1.6.2`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.1...release-1.6.2) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.1...release-1.6.2) ### [`v1.6.1`](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.0...release-1.6.1) [Compare Source](https://togithub.com/greenmail-mail-test/greenmail/compare/release-1.6.0...release-1.6.1)

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