Bump mqtt from 5.14.1 to 5.15.0

Bumps [mqtt](https://github.com/mqttjs/MQTT.js) from 5.14.1 to 5.15.0.
- [Release notes](https://github.com/mqttjs/MQTT.js/releases)
- [Changelog](https://github.com/mqttjs/MQTT.js/blob/main/CHANGELOG.md)
- [Commits](https://github.com/mqttjs/MQTT.js/compare/v5.14.1...v5.15.0)

---
updated-dependencies:
- dependency-name: mqtt
  dependency-version: 5.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

package.json

@@ -15,7 +15,7 @@
     "compression": "^1.8.1",
     "cors": "^2.8.5",
     "express": "^5.2.1",
-    "mqtt": "^5.14.1",
+    "mqtt": "^5.15.0",
     "protobufjs": "^7.5.4",
     "ws": "^8.18.3"
   },