Fix ConfigWarning not calling class method of child classes

[jonathan-eq]

This commit fixes an issue where the parent class ConfigWarning has all methods decorated with staticmethod, rather than classmethod. The class methods should call the child class's method implementation where they are implemented.

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

[eivindjahren]

👍

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.40%. Comparing base (4321e49) to head (2ea48fb).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8845   +/-   ##
=======================================
  Coverage   91.40%   91.40%           
=======================================
  Files         342      343    +1     
  Lines       21034    21086   +52     
=======================================
+ Hits        19226    19274   +48     
- Misses       1808     1812    +4     

Flag	Coverage Δ
cli-tests	39.62% <77.77%> (-0.01%)	⬇️
gui-tests	73.50% <100.00%> (-0.06%)	⬇️
performance-tests	50.16% <77.77%> (-0.07%)	⬇️
unit-tests	79.88% <100.00%> (+0.04%)	⬆️

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