Rake is not required for make bootstrap-packages

What does this Merge Request do and why?

This MR fixes an error when running make bootstrap-packages on a machine without rake installed:

$ make bootstrap-packages
Makefile:28: *** "ERROR: Cannot find 'rake'. Please run 'make bootstrap'.".  Stop.

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 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.