Bump message_bus from 2.1.6 to 2.2.3

Bumps [message_bus](https://github.com/SamSaffron/message_bus) from 2.1.6 to 2.2.3.
- [Release notes](https://github.com/SamSaffron/message_bus/releases)
- [Changelog](https://github.com/SamSaffron/message_bus/blob/master/CHANGELOG)
- [Commits](discourse/message_bus@v2.1.6...v2.2.3)

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

Gemfile.lock

@@ -168,7 +168,7 @@ GEM
       mini_mime (>= 0.1.1)
     marcel (0.3.3)
       mimemagic (~> 0.3.2)
-    message_bus (2.1.6)
+    message_bus (2.2.3)
       rack (>= 1.1.3)
     method_source (0.9.2)
     mimemagic (0.3.3)