roachtest: turn on DistSender circuit breakers for failover chaos tests

Failover chaos tests create assymetric partitions, where DistSender
circuit breakers are useful. It prevents failure modes such as
cockroachdb#123736 (comment).

Fixes cockroachdb#123736

Release note: None

pkg/cmd/roachtest/tests/failover.go

@@ -208,11 +208,14 @@ func runFailoverChaos(ctx context.Context, t test.Test, c cluster.Cluster, readO
 
 	rng, _ := randutil.NewTestRand()
 
-	// Create cluster, and set up failers for all failure modes.
+	// Create cluster, and set up failures for all failure modes.
 	settings := install.MakeClusterSettings()
 	settings.Env = append(settings.Env, "COCKROACH_ENABLE_UNSAFE_TEST_BUILTINS=true")
 	settings.Env = append(settings.Env, "COCKROACH_SCAN_MAX_IDLE_TIME=100ms") // speed up replication
 
+	// DistSender circuit breakers are useful for these chaos tests. Turn them on.
+	settings.ClusterSettings["kv.dist_sender.circuit_breakers.mode"] = "all ranges"
+
 	m := c.NewMonitor(ctx, c.Range(1, 9))
 
 	failers := []Failer{}