CI: Remove use of Ubuntu 20.04

[tautschnig]

GitHub will no longer support ubuntu-20.04 runners after 2025-04-15. Use ubuntu-24.04 or ubuntu-latest instead. This implies that we will no longer release pre-built packages for Ubuntu 20.04.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[TGWDB]

Looks fine.

Only comment/thought is that we're clearly choosing here to prefer latest and then when things break due to latest moving under us we need to fix. This may be slightly more opaque than pinning to a version and being very intentional about needing to upgrade when that version reaches end-of-life or we choose to upgrade.

[tautschnig]

Only comment/thought is that we're clearly choosing here to prefer latest and then when things break due to latest moving under us we need to fix. This may be slightly more opaque than pinning to a version and being very intentional about needing to upgrade when that version reaches end-of-life or we choose to upgrade.

Yes, I was hoping that for the ones where I've now chosen ubuntu-latest that they are largely independent of whatever versions of software the OS provides. This may, as you say, turn out to be false. It's a bit of a gamble with the hope that this will reduce future maintenance burden.

[TGWDB]

Yes, I was hoping that for the ones where I've now chosen ubuntu-latest that they are largely independent of whatever versions of software the OS provides. This may, as you say, turn out to be false. It's a bit of a gamble with the hope that this will reduce future maintenance burden.

As long as we're aware that we made a choice I don't see there being a big concern. 👍

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.37%. Comparing base (fab6710) to head (32d6835).
Report is 6 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8613      +/-   ##
===========================================
+ Coverage    79.63%   80.37%   +0.74%     
===========================================
  Files         1733     1686      -47     
  Lines       197820   206770    +8950     
  Branches     17968       85   -17883     
===========================================
+ Hits        157536   166197    +8661     
- Misses       40284    40573     +289     

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