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

Bumps [posthog-node](https://github.com/PostHog/posthog-js-lite/tree/HEAD/posthog-node) from 4.5.0 to 4.8.1.
- [Release notes](https://github.com/PostHog/posthog-js-lite/releases)
- [Changelog](https://github.com/PostHog/posthog-js-lite/blob/main/posthog-node/CHANGELOG.md)
- [Commits](https://github.com/PostHog/posthog-js-lite/commits/posthog-node-v4.8.1/posthog-node)

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

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

apps/OpenSignServer/package.json

@@ -46,7 +46,7 @@
     "parse-server": "^7.4.0",
     "parse-server-api-mail-adapter": "^4.1.0",
     "pdf-lib": "^1.17.1",
-    "posthog-node": "^4.5.0",
+    "posthog-node": "^4.8.1",
     "ws": "^8.18.0"
   },
   "type": "module",