Executing a rake tasks in gitlab folder from GDK fails due to Bundler environment not being cleared up

What does this merge request do and why?

Ensure we are using Bundler.with_unbundled_env to call rake tasks in gitlab folder

Please check #2002 (closed) for context on why this was necessary

How to set up and validate locally

Run rake gitlab-db-migrate from an installation without asdf.

Then test the same thing in an installation that uses asdf to ensure it still works.

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.

Closes #2002 (closed)