diffTags should not identify existing tags as needing creation

[domwong]

Changes proposed in this pull request:

• diffTags incorrectly returns tags that are the same in oldTags and newTags as needing to be created again. This causes unnecessary calls to CreateTags. Fix this to return only tags that need to be deleted and created

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccAWSInstance.*Tag'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -run=TestAccAWSInstance.*Tag -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAWSInstance_volumeTags
--- PASS: TestAccAWSInstance_volumeTags (186.28s)
=== RUN   TestAccAWSInstance_volumeTagsComputed
--- FAIL: TestAccAWSInstance_volumeTagsComputed (18.64s)
	testing.go:518: Step 0 error: Error applying: 1 error(s) occurred:
		
		* aws_instance.foo: 1 error(s) occurred:
		
		* aws_instance.foo: Error launching source instance: InstanceLimitExceeded: You have requested more instances (1) than your current instance limit of 0 allows for the specified instance type. Please visit http://aws.amazon.com/contact-us/ec2-request to request an adjustment to this limit.
			status code: 400, request id: ad836a70-ded9-4335-94f4-18871c6c96c0
=== RUN   TestAccAWSInstance_forceNewAndTagsDrift
--- PASS: TestAccAWSInstance_forceNewAndTagsDrift (290.62s)
FAIL
FAIL	github.com/terraform-providers/terraform-provider-aws/aws	495.584s
make: *** [testacc] Error 1

Note failures due to account limits

This PR split out from #5072.

[domwong]

@bflad - continuing on from our discussion on #5072 ...

Does this logic potentially exist to handle tag value updates for an existing tag key? Some service APIs do not support updating an existing tag so therefore require delete and create.

I misread this in my initial reply. This update scenario is actually covered in the test case I've added. e.g. updating foo:bar to foo:baz results in corresponding "create" and "remove" calls.

[bflad]

Thanks so much for submitting this @domwong and sorry for the delayed review! 😅 LGTM also running this across a few of our EC2 resource acceptance tests that utilize tagging. 🚀

[bflad]

This has been released in version 1.43.1 of the AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!