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

@@ -3231,6 +3231,7 @@ test('top level test', async (t) => {
 <!-- YAML
 added:
   - v22.2.0
+  - v20.15.0
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 An object containing assertion methods bound to `context`. The top-level