'test_new_bucket_w_ubla' flakes w/ 412 PreconditionFailed

[tseaver]

From this failed run:

____________________________ test_new_bucket_w_ubla ____________________________

storage_client = <google.cloud.storage.client.Client object at 0x7fea45c62510>
buckets_to_delete = [<Bucket: new-w-ubla-1630575370947>], blobs_to_delete = []

 def test_new_bucket_w_ubla(
 storage_client, buckets_to_delete, blobs_to_delete,
 ):
 bucket_name = _helpers.unique_name("new-w-ubla")
 bucket = storage_client.bucket(bucket_name)
 bucket.iam_configuration.uniform_bucket_level_access_enabled = True
 _helpers.retry_429_503(bucket.create)()
 buckets_to_delete.append(bucket)

 bucket_acl = bucket.acl
 with pytest.raises(exceptions.BadRequest):
 bucket_acl.reload()

 bucket_acl.loaded = True # Fake that we somehow loaded the ACL
 bucket_acl.all().grant_read()
 with pytest.raises(exceptions.BadRequest):
> bucket_acl.save()

tests/system/test_bucket.py:711:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
google/cloud/storage/acl.py:546: in save
 self._save(acl, None, client, timeout=timeout)
google/cloud/storage/acl.py:510: in _save
 retry=None,
google/cloud/storage/client.py:454: in _patch_resource
 _target_object=_target_object,
google/cloud/storage/_http.py:78: in api_request
 return call()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <google.cloud.storage._http.Connection object at 0x7fea478ae390>
method = 'PATCH', path = '/b/new-w-ubla-1630575370947'
query_params = {'projection': 'full'}
data = '{"acl": [{"role": "READER", "entity": "allUsers"}]}'
content_type = 'application/json', headers = None, api_base_url = None
api_version = None, expect_json = True, _target_object = None, timeout = 60

 def api_request(
 self,
 method,
 path,
 query_params=None,
 data=None,
 content_type=None,
 headers=None,
 api_base_url=None,
 api_version=None,
 expect_json=True,
 _target_object=None,
 timeout=_DEFAULT_TIMEOUT,
 ):
 """Make a request over the HTTP transport to the API.
 ...
 """
 url = self.build_api_url(
 path=path,
 query_params=query_params,
 api_base_url=api_base_url,
 api_version=api_version,
 )

 # Making the executive decision that any dictionary
 # data will be sent properly as JSON.
 if data and isinstance(data, dict):
 data = json.dumps(data)
 content_type = "application/json"

 response = self._make_request(
 method=method,
 url=url,
 data=data,
 content_type=content_type,
 headers=headers,
 target_object=_target_object,
 timeout=timeout,
 )

 if not 200 <= response.status_code < 300:
> raise exceptions.from_http_response(response)
E PreconditionFailed: 412 PATCH https://storage.googleapis.com/storage/v1/b/new-w-ubla-1630575370947?projection=full&prettyPrint=false: One or more users named in the policy do not belong to a permitted customer.

[tseaver]

@frankyn, @andrewsg, @cojenco I can't see any reason for the error: has something on the back-end changed?