build(deps-dev): bump @vitest/coverage-v8 in /backend

Bumps [@vitest/coverage-v8](https://github.com/vitest-dev/vitest/tree/HEAD/packages/coverage-v8) from 2.1.9 to 4.1.8.
- [Release notes](https://github.com/vitest-dev/vitest/releases)
- [Changelog](https://github.com/vitest-dev/vitest/blob/main/docs/releases.md)
- [Commits](https://github.com/vitest-dev/vitest/commits/v4.1.8/packages/coverage-v8)

---
updated-dependencies:
- dependency-name: "@vitest/coverage-v8"
  dependency-version: 4.1.8
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/package.json

@@ -47,7 +47,7 @@
     "@types/supertest": "^7.2.0",
     "@types/swagger-jsdoc": "^6.0.4",
     "@types/swagger-ui-express": "^4.1.6",
-    "@vitest/coverage-v8": "^2.1.8",
+    "@vitest/coverage-v8": "^4.1.8",
     "eventsource": "^2.0.2",
     "nodemon": "^3.1.11",
     "prisma": "^7.4.1",