test: fix issue with new client overriding previously set api key

[seantcanavan]

I was using the tests as informal documentation so I wasn't sure whether to use the test or the doc tag but since I haven't modified any test output I'm going with doc as it applies more closely to how I was interpreting the code.

if you call sgMail.setClient() before you call sgMail.setApiKey() then everything is great. If you call them in the order that this test does you'll forever get Unauthorized 401 section with data.headers in node_modules/@sendgrid/client/src/classes/client.js createRequest() function not including Bearer Authorization <<YOUR_API_KEY>>

This issue is reproducible whether you set the client / key at the top outside of a typescript class, inside the typescript class' constructor, or inside the function right before the sgMail.send call.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

Here's a GIF of the issue: