Test that CI is skipped for a markdown-only change

[rowlandgeoff]

No description provided.

[mergify]

This pull request does not have a backport label. Could you fix it @rowlandgeoff? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d is the label to automatically backport to the 1./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: bfed3b8

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: bfed3b8