ukify: allow uncompressed kernel images for UNAME detection on aarch64 and riscv64 (#26929)
Uncompressed aarch64 and riscv64 kernels have a different startpoint than x86.
Example output from ukify:
aarch64: NotImplementedError: unknown file format (starts with b'MZ@\xfa')
riscv64: NotImplementedError: unknown file format (starts with b'MZo\x10')
Add check for (b'MZ') to catch both in one call.
Fix:
https://github.com/systemd/systemd/issues/26923