Update ghost to version v6.16.1

[al-lac]

🤖 This is an automated pull request to update ghost to version v6.16.1. This PR must be reviewed and tested before merging.

Auto-generated update considerations:

• Changed from Stripe checkout to Stripe billing portal in v6.14.0, which may affect payment flow configuration or integrations
• Released new admin shell and sidebar in v6.15.0, potentially requiring users to familiarize themselves with new UI layout
• Renamed dev:forward script to dev in v6.15.0, which could affect any custom deployment or development workflows referencing the old script name
• Fixed XSS vulnerabilities in Portal in v6.15.0, security update that should be applied promptly

Original GitHub release notes

[github-actions]

🎉   Linting finished with no errors or warnings   🎉

Thank you for your submission! This is an automated linter that checks for common issues in pull requests to the Umbrel App Store.

[al-lac]

🤖 This is an automated summary of installation tests for ghost:

• ✅ App successfully installed in umbrel-dev instance
• ✅ App successfully listed in umbrel.yaml
• ✅ App UI successfully returns a 200 status code
• 📸 Screenshot of the app:
  

This PR must still be reviewed and tested before merging.

[al-lac]

Tested update on Umbrel dev instance.