## Summary
The code later in this file that checks for slices relies on the stack
of brackets to determine the position. I'm not sure why format strings
were being excluded from this, but the tests still pass with these match
guards removed.
Closes#10278
## Test Plan
~Still needs a test.~ Test case added for this example.
## Summary
This PR makes `whitespace-before-punctuation` (`E203`) compatible with
the formatter by relaxing the rule a bit, as compared to the pycodestyle
implementation. It's also more consistent with PEP 8, which says:
> However, in a slice the colon acts like a binary operator, and should
have equal amounts on either side (treating it as the operator with the
lowest priority).
Closes https://github.com/astral-sh/ruff/issues/7259.
Closes https://github.com/astral-sh/ruff/issues/8642.
## Test Plan
`cargo test`
