Fix subtypes of ConfigWarning not being caught

[jonathan-eq]

This commit fixes the issue where subtypes of ConfigWarning would not be reported in the gui/main.py::_start_inititial_gui_window(...) function.

Approach
⛷️

(Screenshot of new behavior in GUI if applicable)

• 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 91.40%. Comparing base (61c648a) to head (71bb3ce).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8851   +/-   ##
=======================================
  Coverage   91.39%   91.40%           
=======================================
  Files         343      343           
  Lines       21087    21087           
=======================================
+ Hits        19272    19274    +2     
+ Misses       1815     1813    -2     

Flag	Coverage Δ
cli-tests	39.62% <ø> (+<0.01%)	⬆️
gui-tests	73.51% <ø> (ø)
performance-tests	50.21% <ø> (+0.04%)	⬆️
unit-tests	79.87% <ø> (ø)

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[eivindjahren]

superseded by #8857