Rebase Move --package-cache-dir flag to mkosi.conf

It isn't dynamic, so we can have it in the config file.

Rebase of https://invent.kde.org/kde-linux/kde-linux/-/merge_requests/125

build.sh

@@ -68,7 +68,6 @@ mkosi \
     --environment="CI_PIPELINE_URL=${CI_PIPELINE_URL:-https://invent.kde.org}" \
     --environment="VERSION_DATE=${VERSION_DATE}" \
     --image-version="$VERSION" \
-    --package-cache-dir=/var/cache/mkosi.pacman \
     --output-directory=. \
     "$@"
 

mkosi.conf

@@ -23,6 +23,7 @@ KernelCommandLine=
 WithNetwork=true
 # Make sure kernel-install knows where we expect the ESP to be mounted so it can create correct loader entries.
 @Environment=BOOT_MNT=/efi-template
+PackageCacheDirectory=/var/cache/mkosi.pacman
 
 [Runtime]
 Console=gui