Add tests for skip magic trailing comma

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## Summary

This PR adds tests that verify that the magic trailing comma is not respected if disabled in the formatter options. 

Our test setup now allows to create a `<fixture-name>.options.json` file that contains an array of configurations that should be tested. 

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## Test Plan

It's all about tests :) 

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crates/ruff_python_formatter/src/builders.rs

@@ -220,7 +220,7 @@ impl<'fmt, 'ast, 'buf> JoinCommaSeparatedBuilder<'fmt, 'ast, 'buf> {
         if let Some(last_end) = self.last_end.take() {
             if_group_breaks(&text(",")).fmt(self.fmt)?;
 
-            if self.fmt.options().magic_trailing_comma().is_preserve()
+            if self.fmt.options().magic_trailing_comma().is_respect()
                 && matches!(
                     first_non_trivia_token(last_end, self.fmt.context().contents()),
                     Some(Token {