Describe the bug

After #779 was fixed, I'm still seeing some unused substitution key hints when a key is only used in image alt text.

Expected behavior

I should only get hints when a substitution key is actually not used.

Steps to reproduce

Examples:

• docs-content: reports-app (hint / key usage)
  • Note: The hint about release-date being unused is valid!
• kibana: rules-ui (hint / key usage)

Tooling

• docs-builder
• migration tooling
• I'm not sure