Update Ubuntu version in .readthedocs.yaml

[jprestop]

Describe the Task

For all of the METplus component repositories upgrade the version of Ubuntu from 22.04 to 24.04. While 22.04 is still supported, 24.04 is recommended. METviewer is using 20.04, which will definitely need to be changed.

An email with the subject "[Action required] Deprecation of Ubuntu 20.04 LTS build image" indicates:

We are announcing the deprecation of the Ubuntu 20.04 LTS build image (build.os: ubuntu-20.04) on Read the Docs. After June 1, 2026, projects still using this image will fail when building until they are updated to a supported Ubuntu image.

This change keeps our build images current and helps us prepare for Ubuntu 26.04 LTS support. Ubuntu 20.04 LTS is now an older base image and is no longer receiving security updates, so we consider it insecure to continue to offer.

What do I need to do?
Update your .readthedocs.yaml to use a newer supported image. For most projects, we recommend:

build:
os: ubuntu-24.04
Read the Docs currently supports ubuntu-22.04, ubuntu-24.04, and ubuntu-lts-latest for build.os. See all options in the docs: https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os

If your project depends on system packages or tool versions that differ on newer Ubuntu releases, please test your builds early and update before June 1, 2026.

Deprecation timeline
March 30, 2026: Publish deprecation announcement.
Before June 1, 2026: Email maintainers of active projects still using ubuntu-20.04.
June 1, 2026: Remove the ubuntu-20.04 build image.
Are my projects affected?
We found the following projects where you are a maintainer that may be impacted by this change:

metviewer
Read the full announcement: https://about.readthedocs.com/blog/2026/03/ubuntu-20-04-deprecated/

Contact us or reply to this email if you have any questions about this change.

Time Estimate

1-3 days of work

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TBD

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• Select Milestone as a METplus-Wrappers-X.Y.Z version, Consider for Next Release, or Backlog of Development Ideas
• For a METplus-Wrappers-X.Y.Z version, select the METplus-Wrappers-X.Y.Z Development project

Define Related Issue(s)

Consider the impact to the other METplus components.

• METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy

Task Checklist

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• Complete the issue definition above, including the Time Estimate and Funding Source.
• Fork this repository or create a branch of develop.
  Branch name: feature_<Issue Number>_<Description>
• Complete the development and test your changes.
• Add/update log messages for easier debugging.
• Add/update unit tests.
• Add/update documentation.
• Add any new Python packages to the METplus Components Python Requirements table.
• For any new datasets, an entry to the METplus Verification Datasets Guide.
• Push local changes to GitHub.
• Submit a pull request to merge into develop.
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• Define the pull request metadata, as permissions allow.
  Select: Reviewer(s) and Development issue
  Select: Milestone as the next official version
  Select: METplus-Wrappers-X.Y.Z Development project for development toward the next official release
• Iterate until the reviewer(s) accept and merge your changes.
• Delete your fork or branch.
• Close this issue.