Default to RabbitMQ 3.13.7 #891

Job	Run time
unit and integration tests	3m 52s
Build Operator image	1m 33s
Build single-arch ARM64 image	0s
Build single-arch AMD64 image	0s
kubectl rabbitmq tests	2m 39s
Local system tests (stable k8s) (rabbitmq:3.11.0-management)	7m 1s
Local system tests (stable k8s) (rabbitmq:management)	6m 54s
Local system tests (min k8s) (rabbitmq:3.11.0-management)	9m 30s
Local system tests (stable k8s) (pivotalrabbitmq/rabbitmq:main)	7m 41s
Upload manifests to GCS	0s
Local system tests (min k8s) (rabbitmq:management)	8m 10s
Documented example tests	0s
Test upgrade of the operator	0s
Release to GitHub Releases	0s
	47m 20s

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