MNT: migrate inifix-pre-commit hooks

[neutrinoceros]

close #380
Notes

• migrating is essential: neutrinoceros/inifix pre-commit hooks are discontinued beyond v6.1.2
• this new version is smarter: it will exclude pytest.ini automatically, removing the need to write an "anti-pattern" regexp
• if, in the future, you need to exclude other .ini files, you can use args: [--extend-exclude=myfile.ini] (new in this version).