Respect magic trailing comma for set expression (astral-sh#5782)

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## Summary

This PR uses the `join_comma_separated` builder for formatting set
expressions
to ensure the formatting preserves magic commas, if the setting is
enabled.
<!-- What's the purpose of the change? What does it do, and why? -->

## Test Plan
See the fixed black tests

<!-- How was it tested? -->

crates/ruff_python_formatter/src/expression/expr_set.rs

@@ -1,9 +1,10 @@
+use rustpython_parser::ast::{ExprSet, Ranged};
+
+use ruff_python_ast::node::AnyNodeRef;
+
 use crate::expression::parentheses::{parenthesized, NeedsParentheses, OptionalParentheses};
 use crate::prelude::*;
 use crate::FormatNodeRule;
-use ruff_formatter::format_args;
-use ruff_python_ast::node::AnyNodeRef;
-use rustpython_parser::ast::ExprSet;
 
 #[derive(Default)]
 pub struct FormatExprSet;
@@ -14,13 +15,13 @@ impl FormatNodeRule<ExprSet> for FormatExprSet {
         // That would be a dict expression
         assert!(!elts.is_empty());
         // Avoid second mutable borrow of f
-        let joined = format_with(|f| {
-            f.join_with(format_args!(text(","), soft_line_break_or_space()))
-                .entries(elts.iter().formatted())
+        let joined = format_with(|f: &mut PyFormatter| {
+            f.join_comma_separated(item.end())
+                .nodes(elts.iter())
                 .finish()
         });
 
-        parenthesized("{", &format_args![joined, if_group_breaks(&text(","))], "}").fmt(f)
+        parenthesized("{", &joined, "}").fmt(f)
     }
 }