Mark all flaky tests as integration_tests

[eivindjahren]

Make sure running unit tests is reliable.

• 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 91.29%. Comparing base (21af329) to head (a480d40).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8795      +/-   ##
==========================================
- Coverage   91.35%   91.29%   -0.07%     
==========================================
  Files         342      342              
  Lines       20982    20982              
==========================================
- Hits        19169    19155      -14     
- Misses       1813     1827      +14     

Flag	Coverage Δ
cli-tests	39.51% <ø> (-0.05%)	⬇️
gui-tests	73.48% <ø> (ø)
performance-tests	50.06% <ø> (+0.01%)	⬆️
unit-tests	79.81% <ø> (-0.02%)	⬇️

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