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

Bumps [posthog-node](https://github.com/PostHog/posthog-js/tree/HEAD/packages/node) from 5.17.2 to 5.18.0.
- [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/posthog-node@5.18.0/packages/node)

---
updated-dependencies:
- dependency-name: posthog-node
  dependency-version: 5.18.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

apps/OpenSignServer/package-lock.json

@@ -51,7 +51,7 @@
     "parse-server": "^8.6.2",
     "parse-server-api-mail-adapter": "^5.0.2",
     "pdf-lib": "^1.17.1",
-    "posthog-node": "^5.17.2",
+    "posthog-node": "^5.18.0",
     "qrcode": "^1.5.4",
     "rate-limiter-flexible": "^9.0.1",
     "sharp": "^0.34.5",