deploy: Do a full system sync after writing bootloader config

This is just something I noticed on inspection; we should catch any
changes to /boot in the sync(), even though theoretically gio should
have done fdatasync().

src/libostree/ostree-sysroot-deploy.c

@@ -1096,12 +1096,6 @@ ostree_sysroot_write_deployments (OstreeSysroot     *self,
           goto out;
         }
 
-      if (!full_system_sync (cancellable, error))
-        {
-          g_prefix_error (error, "Full sync: ");
-          goto out;
-        }
-
       if (bootloader && !_ostree_bootloader_write_config (bootloader, new_bootversion,
                                                           cancellable, error))
         {
@@ -1109,6 +1103,12 @@ ostree_sysroot_write_deployments (OstreeSysroot     *self,
           goto out;
         }
 
+      if (!full_system_sync (cancellable, error))
+        {
+          g_prefix_error (error, "Full sync: ");
+          goto out;
+        }
+
       if (!swap_bootloader (self, self->bootversion, new_bootversion,
                             cancellable, error))
         {