chore(backend): bump @types/nodemailer in /services/backend

Bumps [@types/nodemailer](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/nodemailer) from 6.4.18 to 7.0.0.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/nodemailer)

---
updated-dependencies:
- dependency-name: "@types/nodemailer"
  dependency-version: 7.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

services/backend/package.json

@@ -51,7 +51,7 @@
     "@types/better-sqlite3": "^7.6.13",
     "@types/fs-extra": "^11.0.4",
     "@types/jest": "^30.0.0",
-    "@types/nodemailer": "^6.4.14",
+    "@types/nodemailer": "^7.0.0",
     "@types/pug": "^2.0.10",
     "@types/supertest": "^6.0.3",
     "@typescript-eslint/eslint-plugin": "^8.36.0",