CI: Update OS version in Read the Docs configuration

[njzjz]

https://about.readthedocs.com/blog/2026/03/ubuntu-20-04-deprecated/

Summary by CodeRabbit

• Chores
  • Updated documentation build environment to use a newer OS image, maintaining compatibility with existing Python toolchain and build configuration.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: ab35d4ab-6578-4808-81d2-60271acc81b6

📥 Commits

Reviewing files that changed from the base of the PR and between baab3e8 and 57a222d.

📒 Files selected for processing (1)

• .readthedocs.yml

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📝 Walkthrough

Walkthrough

Updated the Read the Docs build environment to use Ubuntu 26.04 instead of 26.04. Python version, build steps, package installations, and Sphinx configuration remain unchanged.

Changes

Cohort / File(s)	Summary
Read the Docs Configuration .readthedocs.yml	Updated Ubuntu base image from ubuntu-20.04 to ubuntu-26.04 for the build environment.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: updating the OS version in the Read the Docs configuration from ubuntu-20.04 to ubuntu-26.04.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[Copilot]

Pull request overview

Updates the Read the Docs build environment OS in .readthedocs.yml in response to RTD’s Ubuntu 20.04 deprecation, to keep documentation builds working.

Changes:

• Switch the Read the Docs build os from ubuntu-20.04 to ubuntu-26.04.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.33%. Comparing base (baab3e8) to head (57a222d).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5392      +/-   ##
==========================================
- Coverage   80.33%   80.33%   -0.01%     
==========================================
  Files         819      819              
  Lines       85356    85357       +1     
  Branches     4139     4140       +1     
==========================================
- Hits        68571    68570       -1     
- Misses      15509    15510       +1     
- Partials     1276     1277       +1     

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