[FIX] Fix error bars for threshold averaged ROC curves

[cjgunnar]

Issue

Fixes #7013

Description of changes

Fix typo causing incorrect error bars for threshold averaged ROC curves.

For functions roc_curve_threshold_average and roc_curve_thresh_avg_interp in ROC Analysis widget

Includes

• Code changes
• Tests
• Documentation

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.48%. Comparing base (091e88c) to head (521d623).
Report is 65 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7014      +/-   ##
==========================================
- Coverage   88.48%   88.48%   -0.01%     
==========================================
  Files         332      332              
  Lines       73333    73333              
==========================================
- Hits        64889    64886       -3     
- Misses       8444     8447       +3     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[janezd]

Thanks for noticing, reporting and fixing!

This code is from 2014, but it was migrated from Orange 2, so the bug has likely been here for some 20 years.