doc: update test context.assert

PR-URL: #55186
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Jake Yuesong Li <jake.yuesong@gmail.com>

Author: pmarchini

doc/api/test.md

@@ -2976,6 +2976,7 @@ test('top level test', async (t) => {
 <!-- YAML
 added:
   - v22.2.0
+  - v20.15.0
 -->
 
 An object containing assertion methods bound to `context`. The top-level