Update wp-cli/wp-cli-tests requirement from ^3.1 to ^4.0

Updates the requirements on [wp-cli/wp-cli-tests](https://github.com/wp-cli/wp-cli-tests) to permit the latest version.
- [Release notes](https://github.com/wp-cli/wp-cli-tests/releases)
- [Commits](wp-cli/wp-cli-tests@v3.1.0...v4.0.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -20,7 +20,7 @@
         "wp-cli/extension-command": "^1.2 || ^2",
         "wp-cli/media-command": "^1.1 || ^2",
         "wp-cli/super-admin-command": "^1 || ^2",
-        "wp-cli/wp-cli-tests": "^3.1"
+        "wp-cli/wp-cli-tests": "^4.0"
     },
     "config": {
         "process-timeout": 7200,