Merge pull request juju#16580 from jack-w-shaw/backport_cmr_fix

juju#16580

This PR backports juju#16412. 

Failures are most common on 3.2, but I have also seen related failures on 3.1 (e.g. https://jenkins.juju.canonical.com/job/test-cmr-test-offer-consume-aws/1372/)

For this reason, as well as for the sake on consistency, backport to 2.9

CMR tests continue to fail on CI because of the controller not being cleaned up. This happens because we try to destroy it *before* removing the offers on the model. This patch fixes this.

## Checklist

- [ ] ~Code style: imports ordered, good names, simple structure, etc~
- [ ] ~Comments saying why design decisions were made~
- [ ] ~Go unit tests, with comments saying what you're testing~
- [x] [Integration tests](https://github.com/juju/juju/tree/main/tests), with comments saying what you're testing
- [ ] ~[doc.go](https://discourse.charmhub.io/t/readme-in-packages/451) added or updated in changed packages~

## QA steps

```
./main.sh -v -c aws -p ec2 cmr test_offer_consume
```

tests/suites/cmr/offer_consume.sh

@@ -56,6 +56,8 @@ run_offer_consume() {
 
 	echo "Remove offer"
 	juju remove-relation dummy-sink dummy-offer
+	# wait for the relation to be removed.
+	wait_for null '.applications["dummy-sink"] | .relations'
 	juju remove-saas dummy-offer
 	# wait for saas to be removed.
 	wait_for null '.["application-endpoints"]'
@@ -64,6 +66,7 @@ run_offer_consume() {
 	juju switch "model-offer"
 	wait_for null '.offers."dummy-offer"."total-connected-count"'
 	juju remove-offer "admin/model-offer.dummy-offer" -y
+	wait_for null '.offers'
 
 	echo "Clean up"
 	destroy_model "model-offer"
@@ -117,6 +120,8 @@ run_offer_consume_cross_controller() {
 
 	echo "Remove offer"
 	juju remove-relation dummy-sink dummy-source
+	# wait for the relation to be removed.
+	wait_for null '.applications["dummy-sink"] | .relations'
 	juju remove-saas dummy-source
 	# wait for saas to be removed.
 	wait_for null '.["application-endpoints"]'
@@ -125,6 +130,7 @@ run_offer_consume_cross_controller() {
 	juju switch "${offer_controller}:model-offer"
 	wait_for null '.offers."dummy-offer"."total-connected-count"'
 	juju remove-offer "${offer_controller}:admin/model-offer.dummy-source" -y
+	wait_for null '.offers'
 
 	echo "Clean up"
 	destroy_controller "controller-consume"