Fix dns record set tests

[shuyama1]

This fixes hashicorp/terraform-provider-google#13269

Routing policies referencing internal load balancers need to be added to private zones, therefore, change the parent zone from public to private.

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Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 35 insertions(+), 4 deletions(-))
Terraform Beta: Diff ( 1 file changed, 35 insertions(+), 4 deletions(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2467
Passed tests 2209
Skipped tests: 256
New/modified tests: 2

Action taken

Triggering VCR tests in RECORDING mode for the following tests

TestAccDNSRecordSet_changeRouting|TestAccDNSRecordSet_routingPolicy

Get to know how VCR tests work

[modular-magician]

Tests passed during RECORDING mode:
TestAccDNSRecordSet_changeRouting[Debug log]
TestAccDNSRecordSet_routingPolicy[Debug log]

All tests passed
View the build log or the debug log for each test

[zli82016]

Weird indentations.

[shuyama1]

I guess I was trying to align with ImportStateVerify: true,

[zli82016]

LGTM.