docs(linter): fix invalid code example in rule docs (#27645)

Found by: https://github.com/oxc-project/website/pull/1337

We need valid code example to satisfy `oxc_parser`, otherwise js-in-md code block does not get formatted.

crates/oxc_linter/src/rules/import/no_mutable_exports.rs

@@ -36,10 +36,10 @@ declare_oxc_lint!(
     /// Examples of **incorrect** code for this rule:
     /// ```js
     /// export let count = 2
-    /// export var count = 3
+    /// export var total = 3
     ///
-    /// let count = 4
-    /// export { count }
+    /// let value = 4
+    /// export { value }
     /// ```
     ///
     /// Examples of **correct** code for this rule:

crates/oxc_linter/src/rules/promise/no_return_wrap.rs

@@ -117,7 +117,7 @@ declare_oxc_lint!(
     /// myPromise().then(() => 4)
     /// myPromise().then(function() { return 4 })
     ///
-    /// myPromise().then(() => throw "err")
+    /// myPromise().then(() => { throw "err" })
     /// myPromise().then(function() { throw "err" })
     /// ```
     ///

crates/oxc_linter/src/rules/unicorn/consistent_function_scoping.rs

@@ -90,7 +90,9 @@ declare_oxc_lint!(
     ///	  }
     ///	  return doBar;
     /// }
+    /// ```
     ///
+    /// ```js
     /// function doFoo(foo) {
     ///   const doBar = bar => {
     ///     return bar === 'bar';
@@ -107,7 +109,9 @@ declare_oxc_lint!(
     /// export function doFoo(foo) {
     ///   return doBar;
     /// }
+    /// ```
     ///
+    /// ```js
     /// export function doFoo(foo) {
     ///   function doBar(bar) {
     ///     return bar === 'bar' && foo.doBar(bar);