Updating ubuntu from 20.04 to 24.04, which removes py37, but fixing ci as ubuntu 20.04 is retired.

[thetoddflatline]

Ubuntu 20.04 was retired in April and the ci has been timing out ever since and is labelled has failing on the page.

https://github.blog/changelog/2025-01-15-github-actions-ubuntu-20-runner-image-brownout-dates-and-other-breaking-changes/

We might want to drop support for python 3.7 as it isn't in 24.04.

I've added excludes so 3.7 for ubuntu but left it for windows as it still ruuns there. I can update readme and remove 3.7 everywhere if wanted.

ci now green.

• I signed and returned the Zope Contributor Agreement, and received and accepted an invitation to join a team in the zopefoundation GitHub organization.
• I verified there aren't any other open pull requests for the same change.
• I followed the guidelines in Developer guidelines.
• I successfully ran code quality checks on my changes locally.
• I successfully ran tests on my changes locally.
• If needed, I added new tests for my changes.
• If needed, I added documentation for my changes.
• I included a change log entry in my commits.

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Closes #

[dataflake]

These packaging-related files are not maintained manually in zopefoundation products, but by scripts in the zope.meta package. Someone will get around to do this for ZODB soon, I just don't know when.

[dataflake]

I have created #415 to apply the update scripts we use and fix the specific GHA issue.