Only run sync scripts if we're going to build the image

mkosi/__init__.py

@@ -4829,7 +4829,10 @@ def run_verb(args: Args, images: Sequence[Config], *, resources: Path) -> None:
         with prepend_to_environ_path(config):
             check_tools(config, args.verb)
             images[i] = config = run_configure_scripts(config)
-            run_sync_scripts(config)
+
+            # Only run sync scripts if we're going to build the image.
+            if not (last.output_dir_or_cwd() / last.output).exists() or last.output_format == OutputFormat.none:
+                run_sync_scripts(config)
 
     # The images array has been modified so we need to reevaluate last again.
     last = images[-1]