CI: Fix minor mypy issue

Author: kernc

backtesting/backtesting.py

@@ -167,7 +167,7 @@ def _format_name(name: str) -> str:
             raise ValueError(
                 'Indicators must return (optionally a tuple of) numpy.arrays of same '
                 f'length as `data` (data shape: {self._data.Close.shape}; indicator "{name}" '
-                f'shape: {getattr(value, "shape" , "")}, returned value: {value})')
+                f'shape: {getattr(value, "shape", "")}, returned value: {value})')
 
         if plot and overlay is None and np.issubdtype(value.dtype, np.number):
             x = value / self._data.Close