test: fix test-memory-usage.js for IBMi

Newly added process.memoryUsage.rss() will presumably return 0 on IBMi
the same way process.memoryUsage().rss does. Allow IBMi to skip the new
assertion.

The test was using a mix of `assert()` and `assert.ok()`. This change
makes it consistently use `assert.ok()`.

PR-URL: #36758
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>

test/parallel/test-memory-usage.js

@@ -26,8 +26,11 @@ const assert = require('assert');
 
 const r = process.memoryUsage();
 // On IBMi, the rss memory always returns zero
-if (!common.isIBMi)
+if (!common.isIBMi) {
   assert.ok(r.rss > 0);
+  assert.ok(process.memoryUsage.rss() > 0);
+}
+
 assert.ok(r.heapTotal > 0);
 assert.ok(r.heapUsed > 0);
 assert.ok(r.external > 0);
@@ -39,10 +42,8 @@ if (r.arrayBuffers > 0) {
   const ab = new ArrayBuffer(size);
 
   const after = process.memoryUsage();
-  assert(after.external - r.external >= size,
-         `${after.external} - ${r.external} >= ${size}`);
+  assert.ok(after.external - r.external >= size,
+            `${after.external} - ${r.external} >= ${size}`);
   assert.strictEqual(after.arrayBuffers - r.arrayBuffers, size,
                      `${after.arrayBuffers} - ${r.arrayBuffers} === ${size}`);
 }
-
-assert(process.memoryUsage.rss() > 0);