Skip redundant GitLab Shell setup in Remote development workspace

What does this merge request do and why?

Skip redundant GitLab Shell setup in Remote development workspace

Closes #2108 (closed)

How to set up and validate locally

1. Create a new workspace at https://gitlab.com/-/remote_development/workspaces/new.
2. Choose 2108-skip-gitlab-shell-setup as the Git reference.
3. Click on the workspace.

After the above steps, I confirmed that gitlab-shell-update took 10 seconds, compared to 19 seconds previously.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.