Update wp-phpunit/wp-phpunit requirement from 6.4.* to 6.4.* || 6.5.*

Updates the requirements on [wp-phpunit/wp-phpunit](https://github.com/wp-phpunit/wp-phpunit) to permit the latest version.
- [Commits](wp-phpunit/wp-phpunit@6.4.0...6.5.0)

---
updated-dependencies:
- dependency-name: wp-phpunit/wp-phpunit
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

composer.json

@@ -28,7 +28,7 @@
         "szepeviktor/phpstan-wordpress": "<=1.3.2",
         "php-stubs/wordpress-stubs": "6.4.*",
         "roots/wordpress": "6.4.*",
-        "wp-phpunit/wp-phpunit": "6.4.*",
+        "wp-phpunit/wp-phpunit": "6.4.* || 6.5.*",
         "dealerdirect/phpcodesniffer-composer-installer": "<=1.0.0",
         "wp-coding-standards/wpcs": "<=2.3.0",
         "yoast/phpunit-polyfills": "^1.0.0 || ^2.0.0",