Update erts .readthedocs.yml to point to new locations

[larsevj]

Resolves: #8804

• 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 91.37%. Comparing base (e2d3a90) to head (21c9c53).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8805      +/-   ##
==========================================
+ Coverage   91.29%   91.37%   +0.07%     
==========================================
  Files         342      342              
  Lines       20985    20985              
==========================================
+ Hits        19159    19174      +15     
+ Misses       1826     1811      -15     

Flag	Coverage Δ
cli-tests	39.59% <ø> (+0.05%)	⬆️
gui-tests	73.52% <ø> (ø)
performance-tests	50.08% <ø> (-0.02%)	⬇️
unit-tests	79.82% <ø> (+<0.01%)	⬆️

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