Fix workspace setup failure caused by gdk config warnings

What does this merge request do and why?

This MR fixes workspace setup failures where support/migrate-praefect fails with "flag provided but not defined: -f".

The migrate-praefect script runs $(gdk config get praefect.__praefect_build_bin_path) to get the praefect binary path. But it was also capturing the "GDK setup in progress... Run tail -f..." warning, so praefect received the warning text as arguments and failed on the -f.

Closes #2861 (closed)

How to set up and validate locally

1. Create a workspace with the main branch and see that GDK returns a 502 error
2. Create a workspace with this branch and see that GDK starts successfully

• 
• 

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, 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.