* Update base image to Ubuntu 24.10. This uses a python version where j2cli no
longer works when installed using pip so use the version from Ubuntu instead
which has been patched to work.
* Update shellcheck, pylint, pytest, isort, flake8, black and yamllint to the
latest versions. This closes#502.
* Use a longer expect timeout to fix tests failing when gpg is killed due to
this timeout.
* Explicitly flush gpg-agent's cached passwords to fix failing tests with
latest gnupg. Also clean up after tests to avoid having gpg-agents running
after the test (e.g. when running tests directly without docker).
The new test system is written with py.test. These tests are more
comprehensive, run faster by an order of magnitude, and are far more
maintainable. The tests themselves conform to PEP8.
