backend(deps-dev): bump @testcontainers/postgresql in /apps/backend (#750)

Bumps [@testcontainers/postgresql](https://github.com/testcontainers/testcontainers-node) from 11.14.0 to 12.0.0.
- [Release notes](https://github.com/testcontainers/testcontainers-node/releases)
- [Commits](testcontainers/testcontainers-node@v11.14.0...v12.0.0)

---
updated-dependencies:
- dependency-name: "@testcontainers/postgresql"
  dependency-version: 12.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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Author: dependabot[bot]

apps/backend/package.json

@@ -48,7 +48,7 @@
   },
   "devDependencies": {
     "@faker-js/faker": "^10.1.0",
-    "@testcontainers/postgresql": "^11.13.0",
+    "@testcontainers/postgresql": "^12.0.0",
     "@types/jsonwebtoken": "^9.0.10",
     "@types/node": "^25.5.0",
     "@vitest/coverage-v8": "^4.1.0",