Bump mysql2 from 3.5.2 to 3.6.0 in /backend

Bumps [mysql2](https://github.com/sidorares/node-mysql2) from 3.5.2 to 3.6.0.
- [Release notes](https://github.com/sidorares/node-mysql2/releases)
- [Changelog](https://github.com/sidorares/node-mysql2/blob/master/Changelog.md)
- [Commits](https://github.com/sidorares/node-mysql2/compare/v3.5.2...v3.6.0)

---
updated-dependencies:
- dependency-name: mysql2
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

backend/package.json

@@ -45,7 +45,7 @@
     "crypto-js": "~4.1.1",
     "express": "~4.18.2",
     "maxmind": "~4.3.11",
-    "mysql2": "~3.5.2",
+    "mysql2": "~3.6.0",
     "rust-gbt": "file:./rust-gbt",
     "redis": "^4.6.6",
     "socks-proxy-agent": "~7.0.0",