Increase CI timeout from 2 to 3 hours

What does this merge request do and why?

As an iterative improvement while #1594 (closed) is worked on, we increase the timeout for CI jobs from 2 hours to 3 hours as there are a few jobs that just miss out on the 2 hour limit.

2 hours is too long and so 3 hours is definitely too long, but the aim here is to improve the frequency of passing CI builds in the interim.

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.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.