fix typing

Author: kmuehlbauer

xarray/coding/variables.py

@@ -245,7 +245,7 @@ def _choose_float_dtype(
             maxsize = max(maxsize, np.dtype(type(scale_factor)).itemsize)
         if add_offset and np.issubdtype(type(add_offset), np.floating):
             maxsize = max(maxsize, np.dtype(type(add_offset)).itemsize)
-        return np.dtype(f"float{maxsize * 8}")
+        return np.float32 if maxsize == 4 else np.float64
     # Keep float32 as-is. Upcast half-precision to single-precision,
     # because float16 is "intended for storage but not computation"
     if dtype.itemsize <= 4 and np.issubdtype(dtype, np.floating):