Fix minor formatting bug in error message

gaps/batch.py

@@ -339,7 +339,7 @@ def _check_sets(config, base_dir):
  for fpath in batch_set["files"]:
  if not Path(fpath).exists():
  raise gapsConfigError(
- "Could not find file to modify in batch jobs: {fpath!r}"
+ f"Could not find file to modify in batch jobs: {fpath!r}"
  )
  batch_sets.append(batch_set)