chore(deps): update dependency axllent/mailpit to v1.21.6

Author: renovate-bot

tools/mailpit/manifest.yaml

@@ -4,7 +4,7 @@ name: mailpit
 license:
   name: MIT License
   link: https://github.com/axllent/mailpit/blob/develop/LICENSE
-version: "1.21.5"
+version: "1.21.6"
 check: ${binary} version | cut -d' ' -f2 | tr -d v
 platforms:
 - linux/amd64