Test against WordPress 5.9

[sudip-md]

Is your enhancement related to a problem? Please describe.

Is your enhancement related to a problem? Please describe.

Describe the solution you'd like

• [ ] test WP New Relic on WordPress 5.9
• [ ] open issues for any incompatibilities noted in testing
• [ ] resolve issues identified in testing
• [ ] bump "tested up to" version
• [ ] if code changes needed due to incompatibilities, ship a plugin release, otherwise use "Plugin asset/readme update" action to update "tested up to" version on .org repo

Designs n/a

Describe alternatives you've considered None

Additional context

Designs

No response

Describe alternatives you've considered

No response

Code of Conduct

• [X] I agree to follow this project's Code of Conduct