Bump jsonwebtoken from 8.5.1 to 9.0.0 in /backend

Bumps [jsonwebtoken](https://github.com/auth0/node-jsonwebtoken) from 8.5.1 to 9.0.0.
- [Release notes](https://github.com/auth0/node-jsonwebtoken/releases)
- [Changelog](https://github.com/auth0/node-jsonwebtoken/blob/master/CHANGELOG.md)
- [Commits](https://github.com/auth0/node-jsonwebtoken/compare/v8.5.1...v9.0.0)

---
updated-dependencies:
- dependency-name: jsonwebtoken
  dependency-type: direct:production
...

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

backend/package.json

@@ -17,7 +17,7 @@
     "express-validator": "^6.14.2",
     "handlebars": "^4.7.7",
     "helmet": "^5.1.1",
-    "jsonwebtoken": "^8.5.1",
+    "jsonwebtoken": "^9.0.0",
     "jsrp": "^0.2.4",
     "libsodium-wrappers": "^0.7.10",
     "mongoose": "^6.7.2",