[docs] fix typo (#8013)

## Summary

Fix a typo in the docs for quote style.

> a = "a string without any quotes"
> b = "It's monday morning"
> Ruff will change a to use single quotes when using quote-style =
"single". However, a will be unchanged, as converting to single quotes
would require the inner ' to be escaped, which leads to less readable
code: 'It\'s monday morning'.

It should read "However, **b** will be unchanged".

## Test Plan

N/A.

crates/ruff_workspace/src/options.rs

@@ -2509,7 +2509,7 @@ pub struct FormatOptions {
     /// ```
     ///
     /// Ruff will change `a` to use single quotes when using `quote-style = "single"`. However,
-    /// `a` will be unchanged, as converting to single quotes would require the inner `'` to be
+    /// `b` will be unchanged, as converting to single quotes would require the inner `'` to be
     /// escaped, which leads to less readable code: `'It\'s monday morning'`.
     #[option(
         default = r#"double"#,