Update environment name

What does this MR do?

Update environment name to use CI_COMMIT_REF_SLUG instead of CI_COMMIT_REF_NAME as extraneous symbols creep in

as can be seen in https://dev.gitlab.org/gitlab/charts/components/images/-/jobs/18238087 extra + sign in tag name broke the pipeline.

Related issues

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated
• New dependencies are managed with dependencies.io