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: https://github.com/nodejs/node/pull/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>