Revert "Update action scheduler plugin dependency to ^3.9"

This reverts commit bc31d2b.

Author: bharatpareek

composer.json

@@ -14,7 +14,7 @@
     "php": ">=7.0",
     "ext-json": "*",
     "composer/installers": "~1.0",
-    "woocommerce/action-scheduler": "^3.9"
+    "woocommerce/action-scheduler": "^3.8"
   },
   "require-dev": {
     "automattic/vipwpcs": "^3.0",