Use snapshots for everest export tests

[yngve-sk]

Issue
Resolves #9179

Approach
Short description of the 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 90.77%. Comparing base (3fec61f) to head (647ab03).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9180      +/-   ##
==========================================
+ Coverage   90.74%   90.77%   +0.02%     
==========================================
  Files         352      352              
  Lines       21937    21935       -2     
==========================================
+ Hits        19907    19911       +4     
+ Misses       2030     2024       -6     

Flag	Coverage Δ
cli-tests	39.25% <ø> (+0.01%)	⬆️
gui-tests	71.75% <ø> (+<0.01%)	⬆️
performance-tests	49.36% <ø> (+<0.01%)	⬆️
unit-tests	79.67% <ø> (+0.01%)	⬆️

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[DanSava]

Looks good 👍