Bump express from 4.18.2 to 4.19.2 in /backend

Bumps [express](https://github.com/expressjs/express) from 4.18.2 to 4.19.2.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](https://github.com/expressjs/express/compare/4.18.2...4.19.2)

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

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

backend/package.json

@@ -45,7 +45,7 @@
     "axios": "~1.6.1",
     "bitcoinjs-lib": "~6.1.3",
     "crypto-js": "~4.2.0",
-    "express": "~4.18.2",
+    "express": "~4.19.2",
     "maxmind": "~4.3.11",
     "mysql2": "~3.9.1",
     "rust-gbt": "file:./rust-gbt",