n-api: resolve promise in test

The last promise created by the test for the purposes of making sure
that its type is indeed a promise needs to be resolved so as to avoid
having it left in the pending state at the end of the test.

Backport-PR-URL: #19265
PR-URL: #19245
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

Author: Gabriel Schulhof

test/addons-napi/test_promise/test.js

@@ -45,7 +45,9 @@ common.crashOnUnhandledRejection();
   test_promise.concludeCurrentPromise(Promise.resolve('chained answer'), true);
 }
 
-assert.strictEqual(test_promise.isPromise(test_promise.createPromise()), true);
+const promiseTypeTestPromise = test_promise.createPromise();
+assert.strictEqual(test_promise.isPromise(promiseTypeTestPromise), true);
+test_promise.concludeCurrentPromise(undefined, true);
 
 const rejectPromise = Promise.reject(-1);
 const expected_reason = -1;