Async Sample code needs to await list_approval_requests in accessapproval_v1_generated_access_approval_list_approval_requests_async.py

[ohmayr]

An autogenerated snippet for google-cloud-access-approval needs to await the request call for the sample code to work as expected.

Current behaviour:

    # Make the request
    page_result = client.list_approval_requests(request=request)

Expected behaviour:

    # Make the request
    page_result = await client.list_approval_requests(request=request)