core: bump axllent/mailpit from v1.25.1 to v1.26.0 in /tests/e2e (#14964)

Bumps axllent/mailpit from v1.25.1 to v1.26.0.

---
updated-dependencies:
- dependency-name: axllent/mailpit
  dependency-version: v1.26.0
  dependency-type: direct:production
...

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tests/e2e/docker-compose.yml

@@ -7,7 +7,7 @@ services:
     network_mode: host
     restart: always
   mailpit:
-    image: docker.io/axllent/mailpit:v1.25.1
+    image: docker.io/axllent/mailpit:v1.26.0
     ports:
       - 1025:1025
       - 8025:8025