Ensure print/puts from GDK::Output can be hidden

What does this Merge Request do and why?

This minor MR updates the :hide_stdout tag that can be applied in specs to not only hide output from GDK::Output.puts but also `GDK::Output.print:

$ make rspec
RSpec: ........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
.....................................................................................................................................................................................foo
..................foo
.....................

Finished in 2.39 seconds (files took 0.55032 seconds to load)
868 examples, 0 failures

vs.

RSpec: ....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

Finished in 2.48 seconds (files took 0.49092 seconds to load)
868 examples, 0 failures

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.