Avoid version specific sed syntax

[berland]

The argument to sed prior to this change triggers something in sed version 4.6 or 4.7

Issue
Resolves #9539

Approach
Use simpler grep syntax.

• 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

[JHolba]

tested locally and the new version seems to give the same results as the old 👍

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.87%. Comparing base (0ca408f) to head (97d8363).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9540      +/-   ##
==========================================
+ Coverage   91.84%   91.87%   +0.02%     
==========================================
  Files         433      433              
  Lines       26768    26768              
==========================================
+ Hits        24586    24592       +6     
+ Misses       2182     2176       -6     

Flag	Coverage Δ
cli-tests	39.78% <ø> (ø)
everest-models-test	34.67% <ø> (-0.01%)	⬇️
gui-tests	72.12% <ø> (ø)
integration-test	37.23% <ø> (-0.01%)	⬇️
performance-tests	51.98% <ø> (ø)
test	40.46% <ø> (-0.02%)	⬇️
unit-tests	74.14% <ø> (+0.01%)	⬆️

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