Fix flaky step-integration test

The steps-integration integration tests are occasionally failing with the following error:

ERROR: Job failed (system failure): container exec on "fb713040a3f77c360ea1c8a7829c03c6a9f91cf3189952b03c9ae347df352e78" finished with: executing step request: running job request: rpc error: code = Unavailable desc = connection error: desc = "error reading server preface: io: read/write on closed pipe"

The issue is described and fixed in step-runner!161 (merged). This MR updates the step-runner version referenced here to pick up the fix.