Use macOS-14 runners for ert

[andreas-el]

Building tags

OS	Arch	3.8	3.9	3.10	3.11	3.12
macOS-14	arm64	❌	❌	❌	✅	✅
macOS-14-large	x86_64	❌	❌	❌	✅	✅
macOS-13	x86_64	✅	✅	✅	❌	❌

Testing tags

OS	Arch	3.8	3.12
macOS-14	arm64	❌	✅
macOS-14-large	x86_64	❌	✅
macOS-13	x86_64	✅	❌

Works fine on macOS-14
https://github.com/equinor/ert/actions/runs/8600062307

Use tag macos-latest when doing regular build and test for PR's since we have some included minutes for those specific runners.
Eventually (12 week window or so) these will not point at macos-12, but macos-14.

• 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 tests pass locally (after every commit!)

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 85.19%. Comparing base (7145a29) to head (fac8444).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7592   +/-   ##
=======================================
  Coverage   85.19%   85.19%           
=======================================
  Files         388      388           
  Lines       23338    23338           
  Branches      893      884    -9     
=======================================
  Hits        19883    19883           
+ Misses       3348     3344    -4     
- Partials      107      111    +4     

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