roachtest: deflake c2c driver

PR cockroachdb#105635 fixed some leaky goroutines in the c2c driver, but also revealed a
new bug where a monitor was inadvertently watching the workload node. The
workload node shuts down before the monitor, causing the monitor to fail and
the test to flake. This patch prevents this monitor from watching the workload
node, fixing the infra flake.

Fixes cockroachdb#105595
Fixes cockroachdb#105603
Fixes cockroachdb#105600

pkg/cmd/roachtest/tests/cluster_to_cluster.go

@@ -834,17 +834,18 @@ func registerClusterToCluster(r registry.Registry) {
 			func(ctx context.Context, t test.Test, c cluster.Cluster) {
 				rd := makeReplicationDriver(t, c, sp)
 				rd.setupC2C(ctx, t, c)
+				m := rd.newMonitor(ctx)
 
-				m := c.NewMonitor(ctx)
 				hc := roachtestutil.NewHealthChecker(t, c, rd.crdbNodes())
 				m.Go(func(ctx context.Context) error {
 					require.NoError(t, hc.Runner(ctx))
 					return nil
 				})
-				defer hc.Done()
-
+				defer func() {
+					hc.Done()
+					m.Wait()
+				}()
 				rd.main(ctx)
-				m.Wait()
 			})
 	}
 }