Removed a trailing "`" in the xpack.ml.model_repository parameter

[ivssh]

Removed a trailing "`" in the documentation. This was causing errors in starting the elasticsearch node with bootstrap checks failing.

[github-actions]

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The base branch was changed.

[szabosteve]

@elasticmachine update branch

[mergify]

This pull request is now in conflict. Could you fix it @ivssh? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch <remote-repo>
git checkout -b patch-1 <remote-repo>/patch-1
git merge <remote-repo>/main
git push <remote-repo> patch-1

[szabosteve]

I'm closing this now because I don't have permission to push against the remote of this PR and the docs freeze almost here. Sorry about the inconvenience and thank you for the contribution. I'll add these changes in a separate PR.