build(deps): bump posthog-node in /apps/OpenSignServer

Bumps [posthog-node](https://github.com/PostHog/posthog-js/tree/HEAD/packages/node) from 5.8.4 to 5.9.1.
- [Release notes](https://github.com/PostHog/posthog-js/releases)
- [Changelog](https://github.com/PostHog/posthog-js/blob/main/packages/node/CHANGELOG.md)
- [Commits](https://github.com/PostHog/posthog-js/commits/[email protected]/packages/node)

---
updated-dependencies:
- dependency-name: posthog-node
  dependency-version: 5.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

apps/OpenSignServer/package-lock.json

@@ -49,7 +49,7 @@
     "parse-server": "^8.2.4",
     "parse-server-api-mail-adapter": "^4.1.0",
     "pdf-lib": "^1.17.1",
-    "posthog-node": "^5.8.4",
+    "posthog-node": "^5.9.1",
     "qrcode": "^1.5.4",
     "rate-limiter-flexible": "^7.3.1",
     "sharp": "^0.34.3",