chore(deps): Bump posthog-js from 1.88.3 to 1.121.1

Bumps [posthog-js](https://github.com/PostHog/posthog-js) from 1.88.3 to 1.121.1.
- [Release notes](https://github.com/PostHog/posthog-js/releases)
- [Changelog](https://github.com/PostHog/posthog-js/blob/main/CHANGELOG.md)
- [Commits](PostHog/posthog-js@v1.88.3...v1.121.1)

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

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

package.json

@@ -39,7 +39,7 @@
     "mermaid": "10.1.0",
     "next": "^14.1.3",
     "next-mdx-remote": "^4.4.1",
-    "posthog-js": "^1.88.3",
+    "posthog-js": "^1.121.1",
     "react": "18.3.0-canary-4b2a1115a-20240202",
     "react-dom": "18.2.0",
     "sass": "^1.62.1",