chore(backend): bump @vitest/coverage-v8 in /services/backend

Bumps [@vitest/coverage-v8](https://github.com/vitest-dev/vitest/tree/HEAD/packages/coverage-v8) from 3.2.4 to 4.0.18.
- [Release notes](https://github.com/vitest-dev/vitest/releases)
- [Commits](https://github.com/vitest-dev/vitest/commits/v4.0.18/packages/coverage-v8)

---
updated-dependencies:
- dependency-name: "@vitest/coverage-v8"
  dependency-version: 4.0.18
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

services/backend/package.json

@@ -64,7 +64,7 @@
     "@types/supertest": "^6.0.3",
     "@typescript-eslint/eslint-plugin": "^8.53.1",
     "@typescript-eslint/parser": "^8.53.1",
-    "@vitest/coverage-v8": "^3.2.4",
+    "@vitest/coverage-v8": "^4.0.18",
     "autoprefixer": "^10.4.23",
     "copy-webpack-plugin": "^13.0.1",
     "drizzle-kit": "^0.31.8",