sweet/harnesses: update the version of Cockroachdb benchmarked

This change updates the version of Cockroachdb benchmarked by sweet.
When we submitted a change to how the network is polled in CL 564197
we discovered that older versions of Cockroachdb modify the scheduler
in a way that is incompatable with the submitted change. This updates the
version of Cockroachdb to a version where that incompatibility no
longer exists.

For golang/go#73474
For golang/go#65064

Change-Id: Ifae845e025a5b64ff2cfff65e8c508c999ffbcb4
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/668735
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: cagedmantis

sweet/harnesses/cockroachdb.go

@@ -35,7 +35,7 @@ func (h CockroachDB) Get(gcfg *common.GetConfig) error {
 		gcfg.SrcDir,
 		"https://github.com/cockroachdb/cockroach",
 		"master",
-		"c4a0d997e0da6ba3ebede61b791607aa452b9bbc",
+		"ddf909675a1e0ab9b24d789fc8fa8d9d3e912cf2",
 	)
 }