dns: ignore case changes for DS records

[rjw57]

DS records need case change suppression as with "MX" records.

Fixes hashicorp/terraform-provider-google#9093

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Release Note Template for Downstream PRs (will be copied)

dns: suppress spurious diffs due to case changes in DS records

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I have detected that you are a community contributor, so your PR will be assigned to someone with a commit-bit on this repo for initial review.

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@ScottSuarez, please review this PR or find an appropriate assignee.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 1 insertion(+), 1 deletion(-))
Terraform Beta: Diff ( 1 file changed, 1 insertion(+), 1 deletion(-))
TF Conversion: Diff ( 1 file changed, 1 insertion(+), 1 deletion(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=185967"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccComputeBackendService_internalLoadBalancing You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=185970"