Expand wait condition time for slave selection test (#2604)

## Summary
- extend replication wait time in `slave-selection` test

```
*** [err]: Node #10 should eventually replicate node #5 in tests/unit/cluster/slave-selection.tcl
#10 didn't became slave of #5
```

## Testing
- `./runtest --single unit/cluster/slave-selection`
- `./runtest --single unit/cluster/slave-selection --valgrind`

Signed-off-by: Vitali Arbuzov <Vitali.Arbuzov@proton.me>
Signed-off-by: Binbin <binloveplay1314@qq.com>
Co-authored-by: Binbin <binloveplay1314@qq.com>
Co-authored-by: Harkrishn Patro <bunty.hari@gmail.com>

Author: 3 people

tests/unit/cluster/slave-selection.tcl

@@ -105,7 +105,10 @@ test "Cluster should eventually be up again" {
 
 test "Node #10 should eventually replicate node #5" {
     set port5 [srv -5 port]
-    wait_for_condition 1000 50 {
+    # Valgrind runs are significantly slower and occasionally need more time
+    # for the cluster to propagate the new primary. Use a larger timeout to
+    # avoid spurious failures in slow environments.
+    wait_for_condition 2000 50 {
         ([lindex [R 10 role] 2] == $port5) &&
         ([lindex [R 10 role] 3] eq {connected})
     } else {