sweet/benchmarks/cockroachdb: reduce benchmark concurrency

The benchmark was failing with an `EADDRNOTAVAIL` error, indicating
that the client was exhausting the available network ports. This occurred
because a high number of client connections were being rapidly created
and torn down.

Reducing the concurrency limits the rate of new connections, preventing
port exhaustion and allowing the benchmark to run reliably.

Fixes golang/go#73474

Change-Id: Ib2c0791cc108a54b916c19d28b9ebc21e5ea57fe
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/681595
Auto-Submit: Carlos Amedee <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
TryBot-Bypass: Carlos Amedee <[email protected]>

Author: cagedmantis

sweet/benchmarks/cockroachdb/main.go

@@ -366,7 +366,7 @@ func kvBenchmark(readPercent int, nodeCount int) benchmark {
 			fmt.Sprintf("--read-percent=%d", readPercent),
 			"--min-block-bytes=1024",
 			"--max-block-bytes=1024",
-			"--concurrency=10000",
+			"--concurrency=5000", // Changed from 10000, see go.dev/issue/73474.
 			"--max-rate=30000",
 			// Pre-splitting and scattering the ranges should help stabilize results.
 			"--scatter",