Fix name of rule in example of extend-per-file-ignores in options.rs (#6417)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Fix name of rule in example of `extend-per-file-ignores` in `options.rs`
file.

It was `E401` but in configuration example `E402` was listed. Just a
tiny mismatch.

## Test Plan

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

Just by my eyes :).

crates/ruff/src/settings/options.rs

@@ -596,7 +596,7 @@ pub struct Options {
         default = "{}",
         value_type = "dict[str, list[RuleSelector]]",
         example = r#"
-            # Also ignore `E401` in all `__init__.py` files.
+            # Also ignore `E402` in all `__init__.py` files.
             [tool.ruff.extend-per-file-ignores]
             "__init__.py" = ["E402"]
         "#