WIP: Update Ubuntu in CI
Fixes #451 (closed).
Re-open !295 (closed).
Checklist
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Commits have Signed-off-by:
with name/author being identical to the commit author -
Code modified for feature -
Test suite updated with functionality tests -
Documentation updated / NEWS entry present (for non-trivial changes)
Reviewer's checklist:
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Any issues marked for closing are addressed -
There is a test suite reasonably covering new functionality or modifications -
Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md -
This feature/change has adequate documentation added -
No obvious mistakes in the code