Fix zap command

congrats on the gitlab instance... shame it's not a sourcehut instance, because sending patches via email is much more convenient

anyway, end rant.

This patch fixes a bug

mrtest zap
Traceback (most recent call last):
  File "/usr/bin/mrtest", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/lib/python3.12/site-packages/mrtest/frontend.py", line 76, in main
    origin = mrtest.origin.aports if args.alpine else mrtest.origin.pmaports
                                     ^^^^^^^^^^^
AttributeError: 'Namespace' object has no attribute 'alpine'