Fixed plotter remembering correct tab when switching plot types

[andreas-el]

Issue
Resolves #9451

Approach
This pull request addresses an issue where the plotter was not storing the correct tab when switching between plot types. The approach involves modifying the relevant code to ensure that the correct tab is stored and displayed when the plot type is changed.

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'pytest tests/ert/unit_tests -n logical -m "not integration_test"')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.72%. Comparing base (855c517) to head (99623db).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9635      +/-   ##
==========================================
- Coverage   91.73%   91.72%   -0.01%     
==========================================
  Files         430      430              
  Lines       26639    26649      +10     
==========================================
+ Hits        24437    24444       +7     
- Misses       2202     2205       +3     

Flag	Coverage Δ
cli-tests	39.67% <0.00%> (+0.20%)	⬆️
everest-models-test	34.17% <0.00%> (-0.03%)	⬇️
gui-tests	71.84% <100.00%> (+0.01%)	⬆️
integration-test	38.28% <0.00%> (-0.02%)	⬇️
performance-tests	51.68% <26.31%> (-0.01%)	⬇️
test	39.60% <0.00%> (-0.02%)	⬇️
unit-tests	73.98% <26.31%> (-0.03%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #9635 will not alter performance

_{Comparing andreas-el:fix_plotter_not_selecting_correct_plot_type (99623db) with main (839610b)}

Summary

✅ 24 untouched benchmarks

[berland]

Should index be typed to int here or will that break stuff? If it breaks stuff, should we add an assert on the type of index before using it?

[andreas-el]

I definitely should be int, as the slot is connected to the signal;

void QTabWidget::currentChanged(int index)

Nice catch!

[berland]

Reproduced the bug, and failed to reproduce it after this PR, so looks perfect. Bonus issue discovery in #9657.