CI: Use older compression and file system for macOS disk image

Using older file system (HFS+ instead of APFS) and compression
(lzfse instead of lzma) allows the disk image to be opened on older
versions of macOS, avoiding the cryptic error message that users
are greeted with otherwise.

This is a temporary fix for the still-alive installed base of
Intel-based Macs.

.github/scripts/utils.zsh/create_diskimage

@@ -44,7 +44,7 @@ safe_hdiutil create \
   -volname "${volume_name}" \
   -srcfolder ${source} \
   -ov \
-  -fs APFS \
+  -fs HFS+ \
   -format UDRW \
   temp.dmg
 safe_hdiutil attach \
@@ -70,7 +70,7 @@ log_info "Converting disk image..."
 safe_hdiutil detach /Volumes/${output_name}
 
 safe_hdiutil convert \
-  -format ULMO \
+  -format ULFO \
   -ov \
   -o ${output_name}.dmg temp.dmg