chore(deps): bump php-ds/tests to ^1.6

Author: simPod

composer.json

@@ -15,7 +15,7 @@
         "php": ">= 7.4.0"
     },
     "require-dev": {
-        "php-ds/tests": "^1.5"
+        "php-ds/tests": "^1.6"
     },
     "scripts": {
         "test"   : "php test.php",