doc: document default test-reporter change

Document the change made in nodejs#54548

Author: nicojs

doc/api/test.md

@@ -1051,6 +1051,9 @@ changes:
     - v18.17.0
     pr-url: https://github.com/nodejs/node/pull/47238
     description: Reporters are now exposed at `node:test/reporters`.
+  - version: 23.0.0
+    pr-url: https://github.com/nodejs/node/pull/54548
+    description: The default reporter is now `spec` unconditionally, even when not in a TTY.
 -->
 
 The `node:test` module supports passing [`--test-reporter`][]