Double trigger of woocommerce_subscription_status_changed hook

[kasus]

Describe the bug

woocommerce_subscription_status_changed hook is double triggered when cancelling subscription.
I did some backtrace and I can tell it's caused by this commit 295cba2#diff-bb9ad31c46d815893acb9985f14b98e7573480cfee40ac203639d61063b39f86

Specifically - woocommerce_subscription_status_changed hook triggers WCS_Email_Cancelled_Subscription, which calls for subscription save function, which triggers woocommerce_subscription_status_changed again, because it's in the middle of status_transition loop, and status_transition internal variable hasn't been cleared.