test: add test unknown credential error of process.setgroups

Added test to check ERR_UNKNOWN_CREDENTIAL of process.setgroups to increase
coverage.

Author: Masashi Hirano

test/parallel/test-process-setgroups.js

@@ -45,3 +45,10 @@ assert.throws(
     }
   );
 });
+
+assert.throws(() => {
+  process.setgroups([1, 'fhqwhgadshgnsdhjsdbkhsdabkfabkveyb']);
+}, {
+  code: 'ERR_UNKNOWN_CREDENTIAL',
+  message: 'Group identifier does not exist: fhqwhgadshgnsdhjsdbkhsdabkfabkveyb'
+});