doc: set exit code in custom test runner example

Signed-off-by: Matteo Collina <hello@matteocollina.com>
PR-URL: #51056
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/test.md

@@ -1173,8 +1173,11 @@ import process from 'node:process';
 import path from 'node:path';
 
 run({ files: [path.resolve('./tests/test.js')] })
-  .compose(tap)
-  .pipe(process.stdout);
+ .on('test:fail', () => {
+   process.exitCode = 1;
+ })
+ .compose(tap)
+ .pipe(process.stdout);
 ```
 
 ```cjs
@@ -1183,8 +1186,11 @@ const { run } = require('node:test');
 const path = require('node:path');
 
 run({ files: [path.resolve('./tests/test.js')] })
-  .compose(tap)
-  .pipe(process.stdout);
+ .on('test:fail', () => {
+   process.exitCode = 1;
+ })
+ .compose(tap)
+ .pipe(process.stdout);
 ```
 
 ## `test([name][, options][, fn])`