Bump requirement on tests framework

Author: schlessera

composer.json

@@ -20,7 +20,7 @@
         "wp-cli/db-command": "^1.3 || ^2",
         "wp-cli/entity-command": "^1.3 || ^2",
         "wp-cli/extension-command": "^1.2 || ^2",
-        "wp-cli/wp-cli-tests": "^3.1"
+        "wp-cli/wp-cli-tests": "^3.1.4"
     },
     "config": {
         "process-timeout": 7200,