test: increase coverage for diagnostics_channel

1. test subscribe with invalid args
https://coverage.nodejs.org/coverage-21f2e8859dfbf09f/lib/diagnostics_channel.js.html#L27

2. test create channel with invalid args
https://coverage.nodejs.org/coverage-21f2e8859dfbf09f/lib/diagnostics_channel.js.html#L98

PR-URL: #36602
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Pooja D P <Pooja.D.P@ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yash Ladha <yash@yashladha.in>

Author: Lxxyx

test/parallel/test-diagnostics-channel-object-channel-pub-sub.js

@@ -37,3 +37,7 @@ channel.publish(input);
 // Should not publish after subscriber is unsubscribed
 channel.unsubscribe(subscriber);
 assert.ok(!channel.hasSubscribers);
+
+assert.throws(() => {
+  channel.subscribe(null);
+}, { code: 'ERR_INVALID_ARG_TYPE' });

test/parallel/test-diagnostics-channel-symbol-named.js

@@ -20,3 +20,9 @@ channel.subscribe(common.mustCall((message, name) => {
 }));
 
 channel.publish(input);
+
+{
+  assert.throws(() => {
+    dc.channel(null);
+  }, /ERR_INVALID_ARG_TYPE/);
+}