Fix TestAccBigQueryDatasetAccess_authorizedRoutine and add note about usage

[modular-magician]

Fixes hashicorp/terraform-provider-google#13023

There is more detail on the test failure ticket, but basically a couple of things happening with this change:

• Error when deleting bigquery_dataset_access and modifying bigquery_dataset in same apply terraform-provider-google#13779 was created to capture the underlying issue, to see if we want to prioritize or fix
• Removing the description in our test gets around the underlying issue and allows the test to pass
• The documentation note mentions the underlying issue as a usage limitation

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• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
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Derived from GoogleCloudPlatform/magic-modules#7319