Fix signature of overrides from QAbstractItemModel

[eivindjahren]

To satisfy LSP it should have exactly the same signature as QAbstractItemModel.

• [x] PR title captures the intent of the changes, and is fitting for release notes.
• [x] Added appropriate release note label
• [x] Commit history is consistent and clean, in line with the contribution guidelines.
• [x] Make sure tests pass locally (after every commit!)

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

Attention: Patch coverage is 96.69421% with 4 lines in your changes missing coverage. Please review.

Project coverage is 86.59%. Comparing base (b844a05) to head (e69f709). Report is 2 commits behind head on main.

Files	Patch %	Lines
src/ert/gui/ertwidgets/models/storage_model.py	90.00%	2 Missing :warning:
src/ert/gui/model/progress_proxy.py	96.15%	1 Missing :warning:
src/ert/gui/model/real_list.py	96.55%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #8147 +/- ## ========================================== - Coverage 86.60% 86.59% -0.01% ========================================== Files 383 383 Lines 23778 23813 +35 Branches 628 622 -6 ========================================== + Hits 20593 20622 +29 - Misses 3109 3115 +6 Partials 76 76 ```

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