Test against WordPress 6.0

[vikrampm1]

Is your enhancement related to a problem? Please describe.

Once WordPress 6.0 is released, we'll want to test Distributor to see if any incompatibility issues arise.

Describe the solution you'd like

• test Distributor on WordPress 6.0
• 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

Designs
n/a

Describe alternatives you've considered
none

Additional context
Related: #833, #568, #624, #735, #774.

[lukaspawlik]

@vikrampm1 @jeffpaul I've tested this on 6.0 and all seems to work correctly, I haven't found any issues or problems.

What are next steps with marking this as Tested up to 6.0?

[jeffpaul]

@lukaspawlik there's a header value in readme.txt and the badge in README.md, if you want to open a PR to bump those both to 6.0 that would do it... thanks!