Update to WPCS v3 (#569)

* Update to wp-cli-tests v4 (which requires WPCS v3)

* Fix all autofixable CS issues

* Update `wp-cli/wp-cli-tests`

---------

Co-authored-by: Pascal Birchler <pascalb@google.com>

Author: schlessera

composer.json

@@ -39,7 +39,7 @@
     },
     "require-dev": {
         "roave/security-advisories": "dev-latest",
-        "wp-cli/wp-cli-tests": "^3.0.7"
+        "wp-cli/wp-cli-tests": "^4"
     },
     "suggest": {
         "psy/psysh": "Enhanced `wp shell` functionality"