Some tests broken when run with Pytest v8

[matt-graham]

The scheduled daily tests workflows have been failing since 28th January which coincided with a new Pytest major version release. Checking the logs for the last passing workflow on 27th January, tox installed pytest==7.44 in the test environment while as on the failing runs pytest==8.0.0 was installed.

In the longer term we will want to update the tests so they run on Pytest v8, and probably also have some system for alerting us to deprecations (for example running tests at some regular interval, e.g. weekly, with deprecation warnings filtered to raise an error) so we can be more proactive about fixing them.

For now a quick fix would be to just pin the pytest version in the tox.ini file to 7.4.4

TLOmodel/tox.ini

Lines 28 to 31 in fac71f8

	deps =
	-r{toxinidir}/requirements/base.txt
	pytest
	pytest-cov