fix: stacked bar plot not transparent on click

[rokamu623]

Description

In graphs generated by Plot.create_response_time_stacked_bar_plot() the ability to make the drawing of certain callbacks semi-transparent is not working correctly.

Related links

Jira: https://tier4.atlassian.net/browse/RT2-806

See also:
https://github.com/tier4/CARET_analyze/pull/287/files

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