Fix failing CPU-only tests

[yousefmoazzam]

https://github.com/DiamondLightSource/httomo/actions/runs/9060732934/job/24891044337

Possibly something to do with the python version being used to run httomo:

Run conda run -n httomo pip install pytest plumbum
Requirement already satisfied: pytest in /usr/share/miniconda/envs/httomo/lib/python3.11/site-packages ([8](https://github.com/DiamondLightSource/httomo/actions/runs/9060732934/job/24891044337#step:5:9).2.0)
Collecting plumbum
  Downloading plumbum-1.8.3-py3-none-any.whl.metadata (10 kB)
Requirement already satisfied: iniconfig in /usr/share/miniconda/envs/httomo/lib/python3.11/site-packages (from pytest) (2.0.0)
Requirement already satisfied: packaging in /usr/share/miniconda/envs/httomo/lib/python3.[11](https://github.com/DiamondLightSource/httomo/actions/runs/9060732934/job/24891044337#step:5:12)/site-packages (from pytest) (24.0)
Requirement already satisfied: pluggy<2.0,>=1.5 in /usr/share/miniconda/envs/httomo/lib/python3.11/site-packages (from pytest) (1.5.0)
Downloading plumbum-1.8.3-py3-none-any.whl ([12](https://github.com/DiamondLightSource/httomo/actions/runs/9060732934/job/24891044337#step:5:13)7 kB)
   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 127.6/127.6 kB 7.7 MB/s eta 0:00:00
Installing collected packages: plumbum
Successfully installed plumbum-1.8.3

ImportError while loading conftest '/home/runner/work/httomo/httomo/tests/conftest.py'.
tests/conftest.py:[13](https://github.com/DiamondLightSource/httomo/actions/runs/9060732934/job/24891044337#step:5:14): in <module>
    from httomo.runner.auxiliary_data import AuxiliaryData
httomo/runner/auxiliary_data.py:2: in <module>
    from typing_extensions import TypeAlias
E   ModuleNotFoundError: No module named 'typing_extensions'

The complaint about the typing_extensions module not being available sounds vaguely familiar as being available in an older python version but not in newer versions, or something.