MAINT: Upgrade ruff to v0.6.4 (#3095)
* MNT Upgrade ruff to 0.6.4
Currently used version, 0.2.1, is quite old at this point.
Not a lot needed to be changed:
- Change ruff version in setup.py
- Remove deprecated ignore-init-module-imports option for ruff
- Type comparison should use is and not ==
- Use f-string instead of % formatting
- Some line wrapping and empty lines
* Oops
