Bump the production-dependencies group across 1 directory with 4 updates

Bumps the production-dependencies group with 4 updates in the /backend directory: [dotenv](https://github.com/motdotla/dotenv), [eventsource](https://github.com/EventSource/eventsource), [express](https://github.com/expressjs/express) and [mysql2](https://github.com/sidorares/node-mysql2).


Updates `dotenv` from 16.4.5 to 16.4.7
- [Changelog](https://github.com/motdotla/dotenv/blob/master/CHANGELOG.md)
- [Commits](motdotla/dotenv@v16.4.5...v16.4.7)

Updates `eventsource` from 2.0.2 to 3.0.1
- [Release notes](https://github.com/EventSource/eventsource/releases)
- [Changelog](https://github.com/EventSource/eventsource/blob/main/CHANGELOG.md)
- [Commits](EventSource/eventsource@v2.0.2...v3.0.1)

Updates `express` from 4.21.1 to 4.21.2
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/4.21.2/History.md)
- [Commits](expressjs/express@4.21.1...4.21.2)

Updates `mysql2` from 3.11.4 to 3.11.5
- [Release notes](https://github.com/sidorares/node-mysql2/releases)
- [Changelog](https://github.com/sidorares/node-mysql2/blob/master/Changelog.md)
- [Commits](sidorares/node-mysql2@v3.11.4...v3.11.5)

---
updated-dependencies:
- dependency-name: dotenv
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: production-dependencies
- dependency-name: eventsource
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: production-dependencies
- dependency-name: express
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: production-dependencies
- dependency-name: mysql2
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: production-dependencies
...

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

backend/package.json

@@ -17,11 +17,11 @@
     "bunyan": "^1.8.15",
     "cors": "^2.8.5",
     "cron": "^3.2.1",
-    "dotenv": "^16.4.5",
-    "eventsource": "^2.0.2",
-    "express": "^4.21.1",
+    "dotenv": "^16.4.7",
+    "eventsource": "^3.0.1",
+    "express": "^4.21.2",
     "express-rate-limit": "^7.4.1",
-    "mysql2": "^3.11.4",
+    "mysql2": "^3.11.5",
     "octokit": "^4.0.2",
     "sequelize": "^6.37.5",
     "smee-client": "^2.0.4",