chore: bump up @types/supertest version to v6 (#5376)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [@types/supertest](https://togithub.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/supertest) ([source](https://togithub.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/supertest)) | [`^2.0.16` -> `^6.0.0`](https://renovatebot.com/diffs/npm/@types%2fsupertest/2.0.16/6.0.1) | [![age](https://developer.mend.io/api/mc/badges/age/npm/@types%2fsupertest/6.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/@types%2fsupertest/6.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/@types%2fsupertest/2.0.16/6.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/@types%2fsupertest/2.0.16/6.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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packages/backend/server/package.json

@@ -101,7 +101,7 @@
     "@types/on-headers": "^1.0.3",
     "@types/pretty-time": "^1.1.5",
     "@types/sinon": "^17.0.2",
-    "@types/supertest": "^2.0.16",
+    "@types/supertest": "^6.0.0",
     "@types/ws": "^8.5.10",
     "ava": "^6.0.0",
     "c8": "^8.0.1",