fix: unsupported GPG key for Debian OSI images

This commit fixes an error encountered when mkosi runs apt-get update
during the build of Debian images indicating that the keyring file
provided by debian-archive-keyring package has an unsupported filetype.
The error message is inaccurate as it was discovered with strace that
apt-get executes apt-key, which on its side tries to execute the cmp
command that was actually missing in OSI format container image. The cmp
command is installed with diffutils package (which is arguably an apt
package dependency).

Fix #104

CHANGELOG.md

@@ -16,6 +16,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   images build requirements (#102).
 - Fix `systemd-nspawn` execution error through `mkosi` in OSI format container
   caused by unavailability of DBus system session (#103).
+- Fix GPG keys unsupported filetype error when running `apt-get update` on build
+  of Debian OSI images due to missing `cmp` command (#104).
 
 ## [2.0.0] - 2023-05-05
 

conf/images/osi.mkosi

@@ -8,4 +8,4 @@ Format=directory
 [Content]
 # Docs are useful to get examples from packages and manpages when digging
 WithDocs=yes
-Packages=mkosi,rpm,dnf,apt,debian-keyring,debootstrap,systemd-container
+Packages=mkosi,rpm,dnf,apt,debian-keyring,diffutils,debootstrap,systemd-container