doc: use cjs as block code's type in MockTimers

Use `cjs` instead of `js` to show toggle button between
CJS and ESM because corresponding example using `mjs`
exists.

PR-URL: nodejs#49309
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>
Reviewed-By: Raz Luvaton <rluvaton@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/test.md

@@ -1593,7 +1593,7 @@ import { mock } from 'node:test';
 mock.timers.enable(['setInterval']);
 ```
 
-```js
+```cjs
 const { mock } = require('node:test');
 mock.timers.enable(['setInterval']);
 ```
@@ -1630,7 +1630,7 @@ import { mock } from 'node:test';
 mock.timers.reset();
 ```
 
-```js
+```cjs
 const { mock } = require('node:test');
 mock.timers.reset();
 ```
@@ -1679,7 +1679,7 @@ test('mocks setTimeout to be executed synchronously without having to actually w
 });
 ```
 
-```js
+```cjs
 const assert = require('node:assert');
 const { test } = require('node:test');
 
@@ -1718,7 +1718,7 @@ test('mocks setTimeout to be executed synchronously without having to actually w
 });
 ```
 
-```js
+```cjs
 const assert = require('node:assert');
 const { test } = require('node:test');
 
@@ -1762,7 +1762,7 @@ test('mocks setTimeout to be executed synchronously without having to actually w
 });
 ```
 
-```js
+```cjs
 const assert = require('node:assert');
 const { test } = require('node:test');
 
@@ -1819,7 +1819,7 @@ test('mocks setTimeout to be executed synchronously without having to actually w
 });
 ```
 
-```js
+```cjs
 const assert = require('node:assert');
 const { test } = require('node:test');
 const nodeTimers = require('node:timers');
@@ -1881,7 +1881,7 @@ test('should tick five times testing a real use case', async (context) => {
 });
 ```
 
-```js
+```cjs
 const assert = require('node:assert');
 const { test } = require('node:test');
 const nodeTimersPromises = require('node:timers/promises');
@@ -1947,7 +1947,7 @@ test('runAll functions following the given order', (context) => {
 });
 ```
 
-```js
+```cjs
 const assert = require('node:assert');
 const { test } = require('node:test');