main/grub: correct detection of linux-edge-virt by grub-mkconfig

grub-mkconfig does not correctly handle the linux-edge-virt package when creating /boot/grub.grub.cfg. It incorrectly looks for the file initramfs-virt rather than initramfs-edge-virt due to a regex pattern that behaves differently on Alpine compared to other distros (the regex assumes that kernel package versions and filenames will include the numeric kernel version).

The enclosed patch changes the regex pattern to act correctly on Alpine.