fix(snippet): should emit only one diagnostic (#2650)

crates/biome_js_analyze/src/lint/nursery/no_useless_undefined_initialization.rs

@@ -25,7 +25,7 @@ declare_rule! {
     /// var a = undefined;
     /// ```
     /// ```js,expect_diagnostic
-    /// let b = undefined, c = 1, d = undefined;
+    /// let b = undefined, c = 1, d = 2;
     /// ```
     /// ```js,expect_diagnostic
     /// for (let i = 0; i < 100; i++) {