ci: cirrus: Use --break-system-packages with 'pip install'

Cirrus tests on macos started to fail when installing 'pytest'. Override the pip lock.

Thanks: Andrea Bolognani Signed-off-by: Peter Krempa pkrempa@redhat.com (cherry picked from libvirt commit 743730a83b8a5390b1668e0b432ad9b4deb06483)