WP's unit tests don't yet work with the version of PHPUnit that works with PHP 8

plugins/templates/before-script.yml

@@ -5,7 +5,7 @@ before_script:
   # PHPUnit
   - |
     if [[ $(php -v) =~ "PHP 8." ]]; then
-      composer global require "phpunit/phpunit=7.*"
+      composer global require "phpunit/phpunit=9.*"
     elif [[ $(php -v) =~ "PHP 7." ]]; then
       composer global require "phpunit/phpunit=6.1.*"
     elif [[ $(php -v) =~ "PHP 5.6" ]]; then