Handle service account casing in google_bigquery_dataset_access

[wj-chen]

Fixes hashicorp/terraform-provider-google#19547.

A follow-up to #11477. Service account names come back from the GET API in their original capitalization instead of being normalized to lower-case so need to be specifically handled.

There isn't a good way to add a unit test organically since google_service_account only allows lower-case names and the error came from customers creating upper-case service accounts outside of Terraform.

Release Note Template for Downstream PRs (will be copied)

bigquery: fixed an error which could occur with service account field values containing non-lower-case characters in `google_bigquery_dataset_access`

[github-actions]

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[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.

google provider: Diff ( 1 file changed, 10 insertions(+), 2 deletions(-))
google-beta provider: Diff ( 1 file changed, 10 insertions(+), 2 deletions(-))

[modular-magician]

Tests analytics

Total tests: 120
Passed tests: 110
Skipped tests: 10
Affected tests: 0

Click here to see the affected service packages

• bigquery

🟢 All tests passed!

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[slevenick]

Seems reasonable to me!