Extend Ruff linter config to import sorting with isort

[koeaw]

See Frischmuth's pyproject.toml ("I" is the relevant ruleset for import sorting).

This should get tested locally by team members before adding it to main – there were some (non-obvious) discrepancies between how Ruff picked up on settings on my system vs. how it did (not) on GitHub. ... IIRC my Ruff infered src and known-first-party without them having to be set explicitly.

[b1rger]

there were some (non-obvious) discrepancies between how Ruff picked up on settings on my system vs. how it did (not) on GitHub. ... IIRC my Ruff infered src and known-first-party without them having to be set explicitly

could you explain what exactly that means? I fail to see exactly what exactly I should be testing for