chore(deps): bump axios and @slack/web-api in /backend

Bumps [axios](https://github.com/axios/axios) and [@slack/web-api](https://github.com/slackapi/node-slack-sdk). These dependencies needed to be updated together.

Updates `axios` from 1.6.0 to 1.7.7
- [Release notes](https://github.com/axios/axios/releases)
- [Changelog](https://github.com/axios/axios/blob/v1.x/CHANGELOG.md)
- [Commits](axios/axios@v1.6.0...v1.7.7)

Updates `@slack/web-api` from 6.7.2 to 6.13.0
- [Release notes](https://github.com/slackapi/node-slack-sdk/releases)
- [Commits](https://github.com/slackapi/node-slack-sdk/compare/@slack/web-api@6.7.2...@slack/web-api@6.13.0)

---
updated-dependencies:
- dependency-name: axios
  dependency-type: direct:production
- dependency-name: "@slack/web-api"
  dependency-type: direct:production
...

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

backend/package.json

@@ -43,8 +43,8 @@
     "@nestjs/schedule": "^2.1.0",
     "@nestjs/swagger": "^6.0.4",
     "@nestjs/websockets": "^9.0.0",
-    "@slack/web-api": "^6.7.1",
-    "axios": "^1.6.0",
+    "@slack/web-api": "^6.13.0",
+    "axios": "^1.7.7",
     "bcrypt": "^5.0.1",
     "bull": "^4.8.4",
     "class-transformer": "^0.5.1",