style of `extra_groupstyle_parameters` in signature of `get_tikz_code` wrong

[felinae98]

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According to https://github.com/nschloe/tikzplotlib/blob/450712b4014799ec5f151f234df84335c90f4b9d/src/tikzplotlib/_axes.py#L453-L454 the type of extra_groupstyle_parameters should be list[str], but in https://github.com/nschloe/tikzplotlib/blob/450712b4014799ec5f151f234df84335c90f4b9d/src/tikzplotlib/_save.py#L33 it is dict.