fix comment: the worker half is uncovered, not delegated elsewhere

Author: bavulapati

tests/js-native-api/test_instance_data/testInstanceDataTeardown.js

@@ -1,9 +1,13 @@
 'use strict';
 
 // The delete hook passed to napi_set_instance_data only runs when the
-// environment goes away, so observing it takes a child process. Upstream also
-// runs this in a worker thread; worker threads are a Node.js runtime API, so
-// that variant belongs to the node-api side of the suite.
+// environment goes away, so observing it takes a child process.
+//
+// Upstream also runs the whole test body in a worker thread, which additionally
+// covers instance data being per-environment and the hook running when a
+// secondary environment is torn down. Starting a worker is not expressible in
+// portable ECMAScript, so that half waits on the harness capability proposed in
+// https://github.com/nodejs/node-api-cts/pull/67.
 if (!runtimeFeatures.spawn) {
   skipTest();
 }