distro/rhel85: set bootloader to none for edge

Use the new bootloader config for OSTree deployments to set the
bootloader backend to `none` since we use grub2 and BLS in all
currentlysupported architectures. In fact, not setting it to
`none`, will use the default `auto`, which will result in the
run of `grub2-mkconfig`, which is not what we want and might
even fail for us.

internal/distro/rhel85/stage_options.go

@@ -566,7 +566,8 @@ func ostreeConfigStageOptions(repo string, readOnly bool) *osbuild.OSTreeConfigS
 		Repo: repo,
 		Config: &osbuild.OSTreeConfig{
 			Sysroot: &osbuild.SysrootOptions{
-				ReadOnly: common.BoolToPtr(readOnly),
+				ReadOnly:   common.BoolToPtr(readOnly),
+				Bootloader: "none",
 			},
 		},
 	}