chore: bump compatibility headers for WPGraphQL 1.31.x (#455)

* chore: bump compatibility headers

* tests: fix acceptance suite

* tests: ensure correct env

* ci: list

* ci: pin wp-graphql to v1.32.1

* test: use slugs consistently in AcceptanceCest

* ci: drop unsupported versions

* ci: Try again

* chore: bump phpcs/phpstan and remediate

* dev: update loading hook and fix acceptance test

* chore: phpcs

* chore: cleanup test namespaces

* tests: lint

* tests: fix unit

* tests: fix

* chore: update changelog

Author: justlevine