Update Duo Remote Flows gitlab--duo tag requirement

What does this merge request do and why?

Update Duo Remote Flows gitlab--duo tag requirement

Since gitlab!213431 we will require the gitlab--duo tag to run Duo Agent Platform remote flows.

How to set up and validate locally

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 MR references an issue describing the change.
• This change is backward compatible. If not, include steps to communicate to users.
• Tests added for new functionality. If not, raise an issue to follow-up.
• Observability added/updated (logging, metrics, tracing).
• Documentation added/updated.
• Announcement added for notable changes.
• gdk doctor test added.