Correct docstrings in the pytest-slc

[ahsimb]

These are leftovers from the last PR.

@pytest.fixture(scope='session', autouse=True)
def export_slc_async(slc_builder, use_onprem: bool, use_saas: bool):
    """
    The fixture starts the export() function of the provided LanguageContainerBuilder object as
    an asynchronous task.

    The operation will be skipped if none of the backends is in use **or the container builder
    is not defined**.
    """

@pytest.fixture(scope="session")
def upload_slc(slc_builder, export_slc,
               backend_aware_database_params, backend_aware_bucketfs_params):
    """
    The fixture uploads **the** language container to a database, according to the selected
    backends.
    """

[ckunki]

The first issue is still there. The second is now irrelevant.