Skip 'pack' tests on F40+
    
    On Fedora 40+ and RHEL 10+, we're using zlib-ng rather than
    zlib for compression. As a result, all of the pack tests fail
    due to checking the hashes of the packed data against static
    values that were created with zlib.
    
    https://github.com/libgit2/libgit2/issues/6728
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>