Minor updates to config. files (fixes pre-commit workflow)

[sadielbartholomew]

Mostly (in terms of motivation) to fix a broken reference to the flake8 repository, which moved from GitLab to GitHub at some point recently, which was causing the pre-commit workflow to halt awaiting GitLab authentication. This meant linting was erroring out. Now it should work, both in the sense of not erroring and of passing (locally I have fixed some outstanding black formatting violations). Mostly (in terms of code line changes) the black auto-fixes.

Trivial setup changes therefore no peer review required.

[sadielbartholomew]

The linting CI job has passed, which was the main goal of the PR, so we are all ready to merge. The other jobs (which run the test suite in some form) are erroring, which has raised a separate issue with those workflows (not installing dask which is now essential!) which I might as well also fix here.

[sadielbartholomew]

(Waiting for the 'source-dist-test' jobs to run and complete first, though.)

[sadielbartholomew]

Closing and re-opening to re-trigger all of the CI jobs...

[sadielbartholomew]

OK all good now after I added dask to be installed in the test suite running workflows. They do go on to fail due to numerous sub-failures all or mostly relating ultiamtely to a unmpy-related AttributeError: 'suppress_warnings' object has no attribute '_orig_show', but that will need investigating separately, so I can close this. (It looks like numpy/numpy#8413 will help us work out how to fix that, though.)