Fix diffTags to actually create a diff instead of unnecessarily recre…

[fbreckle]

…ating existing tags.

Solves Issue #6363

Changes proposed in this pull request:

Modify diffTags to behave as explained in its comment:

// diffTags takes our tags locally and the ones remotely and returns
// the set of tags that must be created, and the set of tags that must
// be destroyed.

Many similar functions exist for other aws elements, which all seem to have the same erroneous behavior and can be fixed analogously.

[bflad]

Thanks for submitting this, @fbreckle! Could you adding a covering unit test in TestDiffTags?

https://github.com/terraform-providers/terraform-provider-aws/blob/master/aws/tags_test.go#L14

[fbreckle]

done!

[bflad]

Thanks so much, @fbreckle! In doing my pre-merge sweep of existing PRs I caught #5108 which is also doing a similar update as this PR. To be fair to both your contributions, I'm pulling in the #5108 code and this PR's additional testing. LGTM after acceptance testing this against a few of our EC2 resource tests. 🚀

[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!