allow pre-commit run --files ... against unmerged files

pre_commit/commands/run.py

@@ -333,7 +333,7 @@ def run(
     stash = not args.all_files and not args.files
 
     # Check if we have unresolved merge conflict files and fail fast.
-    if _has_unmerged_paths():
+    if stash and _has_unmerged_paths():
         logger.error('Unmerged files.  Resolve before committing.')
         return 1
     if bool(args.from_ref) != bool(args.to_ref):