Bump @etherpad/express-session from 1.18.2 to 1.18.4 (#6601)

Bumps [@etherpad/express-session](https://github.com/ether/express-session) from 1.18.2 to 1.18.4.
- [Changelog](https://github.com/ether/express-session/blob/main/HISTORY.md)
- [Commits](https://github.com/ether/express-session/commits/v1.18.4)

---
updated-dependencies:
- dependency-name: "@etherpad/express-session"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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src/package.json

@@ -30,7 +30,7 @@
     }
   ],
   "dependencies": {
-    "@etherpad/express-session": "^1.18.2",
+    "@etherpad/express-session": "^1.18.4",
     "async": "^3.2.6",
     "axios": "^1.7.4",
     "cookie-parser": "^1.4.6",