Re-enable tests in datalabeling

[parthea]

Transferring this issue from https://github.com/googleapis/python-datalabeling/issues/53 to enable tests in https://github.com/GoogleCloudPlatform/python-docs-samples/tree/main/datalabeling.

It seems like the dataset is considered empty for label_text_test.py::test_label_text. the test backend is throwing DeadlineExceeded for manage_dataset_test.py::test_list_dataset.

Several tests are skipped. As an example, see below

https://github.com/GoogleCloudPlatform/python-docs-samples/blob/f735455f1faaf7a149c7d16f300bd02cace40302/datalabeling/snippets/manage_dataset_test.py#L87-L97