Fix make targets for shell script linting

What does this MR do and why?

I noticed that the shell scripting job wasn't working in CI/CD pipelines: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/5905437288, so have fixed that (https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/5945076362).

While here, I've also cleared some yaml warnings: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/5905437289. Fixes: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/5945076365.

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