Something has gone seriously wrong: import_mok_state() failed

[Lonni J Friedman]

I'm attempting to install Fedora 30 on an old Macbook Air (7.1), and
as soon as it tries to boot from the USB stick, it fails, printing the
following errors:
######
Failed to start MokManager: Not Found
Something has gone seriously wrong: import_mok_state() failed
######

after which the laptop powers off on its own.  This is before any sort
of GRUB menu or anything interactive appears.  Its literally this bug:
https://bugs.centos.org/view.php?id=15522

But I'm puzzled how the Fedora 30 grub bits could be broken in this fashion?