feat: add scope to default credentials

[davidspek]

This PR cloudPlatformScope when finding default credentials. When using Workload Identity Federation the credentials JSON has type: external_account and can possibly also have a service_account_impersonation_url value set. This is the case when using the google-github-actions/auth@v2 GitHub Action. In such cases, the cloudPlatformScope needs to be included otherwise the request will error with the following unhelpful error:

oauth2/google: status code 400: {
  "error": {
    "code": 400,
    "message": "Request contains an invalid argument.",
    "status": "INVALID_ARGUMENT"
  }
}

This issue is somewhat related to golang/oauth2#537

This PR also updates the oauth2 library to the latest version.

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: davidspek
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[google-oss-prow]

Hi @davidspek. Thanks for your PR.

I'm waiting for a GoogleCloudPlatform member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[lindsayismith]

/ok-to-test