chore(deps): bump @posthog/nextjs-config from 1.2.0 to 1.3.9 (#5593)

Bumps [@posthog/nextjs-config](https://github.com/PostHog/posthog-js/tree/HEAD/packages/nextjs-config) from 1.2.0 to 1.3.9.
- [Release notes](https://github.com/PostHog/posthog-js/releases)
- [Changelog](https://github.com/PostHog/posthog-js/blob/main/packages/nextjs-config/CHANGELOG.md)
- [Commits](https://github.com/PostHog/posthog-js/commits/@posthog/[email protected]/packages/nextjs-config)

---
updated-dependencies:
- dependency-name: "@posthog/nextjs-config"
  dependency-version: 1.3.9
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

apps/frontend/package.json

@@ -48,7 +48,7 @@
     "@monaco-editor/react": "^4.7.0",
     "@opensource-observer/utils": "workspace:*",
     "@plasmicapp/loader-nextjs": "^1.0.435",
-    "@posthog/nextjs-config": "^1.2.0",
+    "@posthog/nextjs-config": "^1.3.9",
     "@radix-ui/react-accordion": "^1.2.12",
     "@radix-ui/react-checkbox": "^1.3.3",
     "@radix-ui/react-collapsible": "^1.1.12",