tests/functional/m68k: Avoid ResourceWarning in the nextcube test

Since commit c3fd296cf7b1 ("functional: always enable all python
warnings") we enabled more warnings for the functional tests. This
triggers now a warning in the nextcube test:

 tests/functional/m68k/test_nextcube.py:47: ResourceWarning:
  unclosed file <_io.BufferedReader name='tests/functional/m68k/test_nextcube.NextCubeMachine.test_bootrom_framebuffer_size/scratch/dump.ppm'>
   width, height = Image.open(screenshot_path).size

Use a proper "with" context to avoid it.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250829142000.62320-1-thuth@redhat.com>
1 file changed