Fix test for IAM get/set.

[crwilcox]

__________________ TestStorageBuckets.test_get_set_iam_policy __________________

self = <tests.system.TestStorageBuckets testMethod=test_get_set_iam_policy>

    def test_get_set_iam_policy(self):
        import pytest
        from google.cloud.storage.iam import STORAGE_OBJECT_VIEWER_ROLE
        from google.api_core.exceptions import BadRequest, PreconditionFailed

        bucket_name = "iam-policy" + unique_resource_id("-")
        bucket = retry_429_503(Config.CLIENT.create_bucket)(bucket_name)
        self.case_buckets_to_delete.append(bucket_name)
        self.assertTrue(bucket.exists())

        policy_no_version = bucket.get_iam_policy()
        self.assertEqual(policy_no_version.version, 1)

        policy = bucket.get_iam_policy(requested_policy_version=3)
        self.assertEqual(policy, policy_no_version)

        member = "serviceAccount:{}".format(Config.CLIENT.get_service_account_email())

        BINDING_W_CONDITION = {
            "role": STORAGE_OBJECT_VIEWER_ROLE,
            "members": {member},
            "condition": {
                "title": "always-true",
                "description": "test condition always-true",
                "expression": "true",
            },
        }
        policy.bindings.append(BINDING_W_CONDITION)

        with pytest.raises(
            PreconditionFailed, match="enable uniform bucket-level access"
        ):
            bucket.set_iam_policy(policy)

        bucket.iam_configuration.uniform_bucket_level_access_enabled = True
        bucket.patch()

        policy = bucket.get_iam_policy(requested_policy_version=3)
        policy.bindings.append(BINDING_W_CONDITION)

        with pytest.raises(BadRequest, match="at least 3"):
            bucket.set_iam_policy(policy)

        policy.version = 3
        returned_policy = bucket.set_iam_policy(policy)
        self.assertEqual(returned_policy.version, 3)
        self.assertEqual(returned_policy.bindings, policy.bindings)

        with pytest.raises(
            BadRequest, match="cannot be less than the existing policy version"
        ):
>           bucket.get_iam_policy()
E           Failed: DID NOT RAISE <class 'google.api_core.exceptions.BadRequest'>

tests/system.py:315: Failed