doc: clarify execution of after hook on test suite completion

The `after` hook now explicitly mentions that it is executed once after
all the tests in a test suite have completed, regardless of whether the
tests passed or failed. This ensures that cleanup tasks or actions
specified in the after hook are guaranteed to run.

Refs: nodejs#50901
PR-URL: nodejs#51523
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>

doc/api/test.md

@@ -1420,6 +1420,9 @@ describe('tests', async () => {
 });
 ```
 
+**Note:** The `after` hook is guaranteed to run,
+even if tests within the suite fail.
+
 ## `beforeEach([fn][, options])`
 
 <!-- YAML
@@ -1473,6 +1476,9 @@ added:
 This function is used to create a hook running
 after each subtest of the current test.
 
+**Note:** The `afterEach` hook is guaranteed to run after every test,
+even if any of the tests fail.
+
 ```js
 describe('tests', async () => {
   afterEach(() => console.log('finished running a test'));