Don't format trailing comma for lambda arguments (#5946)

**Summary** lambda arguments don't have parentheses, so they shouldn't
get a magic trailing comma either. This fixes some unstable formatting

**Test Plan** Added a regression test.

89 (from previously 145) instances of unstable formatting remaining.

```
$ cargo run --bin ruff_dev --release -- format-dev --stability-check --error-file formatter-ecosystem-errors.txt --multi-project target/checkouts > formatter-ecosystem-progress.txt
$ rg "Unstable formatting" target/formatter-ecosystem-errors.txt | wc -l
89
```

Closes #5892

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.py

@@ -66,3 +66,12 @@ a = (
 # formatting
 (lambda:(#
 ),)
+
+# lambda arguments don't have parentheses, so we never add a magic trailing comma ...
+def f(
+    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa: bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb = lambda x: y,
+):
+    pass
+
+# ...but we do preserve a trailing comma after the arguments
+a = lambda b,: 0

crates/ruff_python_formatter/resources/test/fixtures/ruff/skip_magic_trailing_comma.py

@@ -20,3 +20,10 @@
     "seventh entry",
     "eighth entry",
 )
+
+# Regression test: Respect setting in Arguments formatting
+def f(a): pass
+def g(a,): pass
+
+x1 = lambda y: 1
+x2 = lambda y,: 1