build(deps): bump stalwartlabs/stalwart

Bumps stalwartlabs/stalwart from v0.16.5 to v0.16.6.

---
updated-dependencies:
- dependency-name: stalwartlabs/stalwart
  dependency-version: v0.16.6
  dependency-type: direct:production
...

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

docker/infrastructure/mail/stalwart/docker-compose.yml

@@ -1,6 +1,6 @@
 services:
   stalwart:
-    image: stalwartlabs/stalwart:v0.16.5
+    image: stalwartlabs/stalwart:v0.16.6
     container_name: stalwart
     networks:
       - default