mkosi refuses to run a non-executable postinst. git was tracking it
as 100644 because it was added from Windows (no POSIX exec bit on the
FS), so CI saw a non-executable file even though WSL/Linux had been
treating it fine locally. Same fix applied earlier to install.sh +
pxe-setup.sh.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>