Warning: "FutureWarning: 'H' is deprecated"

Hi, first of all thanks for the integration!

I have the following warning in my log:

```
2025-01-18 13:51:26.804 WARNING (MainThread) [py.warnings] /config/custom_components/stromnetzgraz/sensor.py:211: FutureWarning: 'H' is deprecated and will be removed in a future version, please use 'h' instead.
  df.groupby(pandas.Grouper(freq="H", key="readTime"))
```