cmd/bench: set runstamp for subrepo tests

For golang/go#53538.

Change-Id: Ic68861b65a7b5cd259ab6c8c82a10a08323f1a6d
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/459096
Auto-Submit: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
1 file changed