chore: bump up c8 version to v9 (#5505)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [c8](https://togithub.com/bcoe/c8) | [`^8.0.1` -> `^9.0.0`](https://renovatebot.com/diffs/npm/c8/8.0.1/9.0.0) | [![age](https://developer.mend.io/api/mc/badges/age/npm/c8/9.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/c8/9.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/c8/8.0.1/9.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/c8/8.0.1/9.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>bcoe/c8 (c8)</summary>

### [`v9.0.0`](https://togithub.com/bcoe/c8/blob/HEAD/CHANGELOG.md#900-2024-01-03)

[Compare Source](https://togithub.com/bcoe/c8/compare/v8.0.1...v9.0.0)

##### ⚠ BREAKING CHANGES

-   **build:** minimum Node.js version is now 14.14.0

##### Features

-   **build:** minimum Node.js version is now 14.14.0 ([2cdc86b](2cdc86bd0a))
-   **deps:** update foreground-child to promise API ([#&#8203;512](https://togithub.com/bcoe/c8/issues/512)) ([b46b640](b46b640127))
-   **deps:** use Node.js built in rm ([2cdc86b](2cdc86bd0a))

</details>

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packages/backend/server/package.json

@@ -104,7 +104,7 @@
     "@types/supertest": "^6.0.0",
     "@types/ws": "^8.5.10",
     "ava": "^6.0.0",
-    "c8": "^8.0.1",
+    "c8": "^9.0.0",
     "nodemon": "^3.0.1",
     "sinon": "^17.0.1",
     "supertest": "^6.3.3",