doc: fix test runner examples

PR-URL: nodejs/node#46565
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
(cherry picked from commit be4921474671fb15f0e62adfe2f37253d07eca02)

README.md

@@ -801,7 +801,7 @@ before each subtest of the current suite.
 
 ```js
 describe('tests', async () => {
-  beforeEach(() => t.diagnostics('about to run a test'));
+  beforeEach(() => console.log('about to run a test'));
   it('is a subtest', () => {
     assert.ok('some relevant assertion here');
   });
@@ -826,7 +826,7 @@ after each subtest of the current test.
 
 ```js
 describe('tests', async () => {
-  afterEach(() => t.diagnostics('about to run a test'));
+  afterEach(() => console.log('about to run a test'));
   it('is a subtest', () => {
     assert.ok('some relevant assertion here');
   });