Fix leading comment formatting for lambdas with multiple parameters (#21879)
## Summary
This is a follow-up to #21868. As soon as I started merging #21868 into
#21385, I realized that I had missed a test case with `**kwargs` after
the `*args` parameter. Such a case is supposed to be formatted on one
line like:
```py
# input
(
lambda
# comment
*x,
**y: x
)
# output
(
lambda
# comment
*x, **y: x
)
```
which you can still see on the
[playground](https://play.ruff.rs/bd88d339-1358-40d2-819f-865bfcb23aef?secondary=Format),
but on `main` after #21868, this was formatted as:
```py
(
lambda
# comment
*x,
**y: x
)
```
because the leading comment on the first parameter caused the whole
group around the parameters to break.
Instead of making these comments leading comments on the first
parameter, this PR makes them leading comments on the parameters list as
a whole.
## Test Plan
New tests, and I will also try merging this into #21385 _before_ opening
it for review this time.
<hr>
(labeling `internal` since #21868 should not be released before some
kind of fix)
ruff
f3714fd3 - Fix leading comment formatting for lambdas with multiple parameters (#21879)
