chore: bump up @nestjs/schedule version to v6 (#11780)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [@nestjs/schedule](https://redirect.github.com/nestjs/schedule) | [`^5.0.1` -> `^6.0.0`](https://renovatebot.com/diffs/npm/@nestjs%2fschedule/5.0.1/6.0.0) | [![age](https://developer.mend.io/api/mc/badges/age/npm/@nestjs%2fschedule/6.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/@nestjs%2fschedule/6.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/@nestjs%2fschedule/5.0.1/6.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/@nestjs%2fschedule/5.0.1/6.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>nestjs/schedule (@&#8203;nestjs/schedule)</summary>

### [`v6.0.0`](https://redirect.github.com/nestjs/schedule/releases/tag/6.0.0)

[Compare Source](https://redirect.github.com/nestjs/schedule/compare/5.0.1...6.0.0)

#### What's Changed

-   fix(deps): update dependency cron to v4 by [@&#8203;renovate](https://redirect.github.com/renovate) in [https://github.com/nestjs/schedule/pull/1899](https://redirect.github.com/nestjs/schedule/pull/1899)

**Full Changelog**: https://github.com/nestjs/schedule/compare/5.0.1...6.0.0

</details>

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### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

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packages/backend/server/package.json

@@ -44,7 +44,7 @@
     "@nestjs/graphql": "^13.0.4",
     "@nestjs/platform-express": "^11.0.12",
     "@nestjs/platform-socket.io": "^11.0.12",
-    "@nestjs/schedule": "^5.0.1",
+    "@nestjs/schedule": "^6.0.0",
     "@nestjs/throttler": "^6.4.0",
     "@nestjs/websockets": "^11.0.12",
     "@node-rs/argon2": "^2.0.2",