Bar chart labels are not styled properly

Hi!

If you render a bar chart with *these* options:

```python
config = pygal.Config()
config.print_values = True
config.print_values_position = "top"
config.style = pygal.style.DarkStyle
config.value_colors = ('white',)
```

then the value color is not set properly. On output the style for the labels does not have any label color.

Reproduce the issue with the Python configuration shown and inspect how bar-chart value labels receive their styles. Done means labels rendered with print_values_position="top" use the configured value_colors entry, including with DarkStyle; the payload names no files or tests to run.

Written by the indexing model from the issue text.