spanner: fix timeout+staleness bound for test
spanner: fix timeout+staleness bound for test

Make the timeout value for the test correspond with the staleness
bound value that is set during the test to prevent flaky failures.

Fixes #1890

Change-Id: I6baac2d9fe9d7ccdd547b33957ceed8fc01be613
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/55591
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Hengfeng Li <b0a1bcb38cb78116cc20da5a7cacec7b885825f4@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go