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What happened?

In fact, that's not a real bug report, but a suggestion about safe design to plot with scanpy.

It may happen when our celltype name is too long to show in the plotting figure.
The problem happens here:

It cut off the string in functions dotplot/matrixplot(var_group_labels=) , as the function _plot_var_groups_brackets(group_labels=).

So, when we use code like the sample, the veryvery long labels will be cut off & we got an Error
Because Var celltype_order is a list, and function _plot_var_groups_brackets (PATH: scanpy/plotting/_baseplot_class.py) will affect the string in list,
then if affect the celltype_order itself, so

when called with the categories_order, it has been changed by _plot_var_groups_brackets, then the Error happened.

I suggest to add one copy, for parameter group_labels in function _plot_var_groups_brackets
It may help someone are not so skillful on coding, to solve the problem maybe happen.

For example: add the code group_labels = copy.deepcopy(group_labels) at the top of function _plot_var_groups_brackets

Thank you very much for your attention

Minimal code sample

adata: any anndata
markers: gene list include in var_names
group: obs key
celltype_order = ['short', 'veryveryverylong_name', 'others', ...]

sc.pl.dotplot(
	adata, markers, group, show=False, swap_axes=True,
	categories_order=celltype_order, var_group_labels=celltype_order, var_group_positions=pos_markers,
)

Error output

KeyError: "['veryvery.'] not in index"
# (in fact the 'veryvery.' comes from the 'veryveryverylong_name' in celltype_order )

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