TestGraphsyncRoundTripIgnoreNBlocks very flaky failing on Go 1.18 x86

[rvagg]

Kind of weird, and the failure outcomes are not consistent: macos seems OK, Windows seems to consistently fail, Linux seems to be flaky.

Ref: #378

[rvagg]

also fails with the race detector, though it seems less often than x86: https://github.com/ipfs/go-graphsync/runs/6918407647

I can't repro it locally, even looping on that specific test or all integration tests together. Perhaps a container speed thing in CI.