Update definitions for PHPUnit 8.5

Author: MGatner

.gitignore

@@ -123,4 +123,5 @@ nb-configuration.xml
 .vscode/
 
 /results/
-/phpunit*.xml
+/phpunit*.xml
+/.phpunit.*.cache

composer.json

@@ -16,7 +16,7 @@
     "require-dev": {
         "codeigniter4/codeigniter4-standard": "^1.0",
         "mikey179/vfsstream": "1.6.*",
-        "phpunit/phpunit": "^7.0",
+        "phpunit/phpunit": "^8.5",
         "squizlabs/php_codesniffer": "^3.3"
     },
     "autoload": {