See if this fixes the php fatal error

As Kaspars mentioned, the Travis build for
xwp#89
had a fatal error for phpunit:
https://travis-ci.com/github/xwp/block-scaffolding-wp/builds/225499204#L428

Author: kienstra

composer.json

@@ -12,10 +12,10 @@
   "require-dev": {
     "10up/wp_mock": "0.4.2",
     "dealerdirect/phpcodesniffer-composer-installer": "0.7.1",
-    "mockery/mockery": "1.3.1",
+    "mockery/mockery": "1.4.3",
     "php-coveralls/php-coveralls": "2.2.0",
     "phpcompatibility/phpcompatibility-wp": "2.1.0",
-    "phpunit/phpunit": "8.5.2",
+    "phpunit/phpunit": "9.2.0",
     "wp-coding-standards/wpcs": "2.3.0",
     "wpsh/local": "0.2.3"
   },