fix(test): pin scylla-bench to fix multidc counter test

We face the issue with disconnecting from cluster after simple table
modifications in scylla-bench (counters multidc test):
scylladb/scylla-bench#114

It was proven it behaves correctly when s-b is in version 0.1.3.
This commit pins s-b for couters multidc test.

test-cases/longevity/longevity-counters-multidc.yaml

@@ -22,3 +22,7 @@ server_encrypt: true
 internode_encryption: 'dc'
 
 use_legacy_cluster_init: false
+
+# pin s-b version to mitigate https://github.com/scylladb/scylla-bench/issues/114
+stress_image:
+  scylla-bench: 'scylladb/hydra-loaders:scylla-bench-v0.1.3'