fix(c-s): use 5.4.6 image for c-s

Recently scylla-tools package is not installed in scylladb docker
images. This makes c-s not being installed in docker images we use for
loaders.

Workaround by pinning version with c-s installed.

workarounds: scylladb#7430

defaults/test_default.yaml

@@ -209,7 +209,7 @@ stress_image:
   ndbench: 'scylladb/hydra-loaders:ndbench-jdk8-20210720'
   ycsb: 'scylladb/hydra-loaders:ycsb-jdk8-20220918'
   nosqlbench: 'scylladb/hydra-loaders:nosqlbench-4.15.49'
-  cassandra-stress: '' # default would be same version as scylla under test
+  cassandra-stress: 'scylladb/scylla:5.4.6' # empty default would be same version as scylla under test
   scylla-bench: 'scylladb/hydra-loaders:scylla-bench-v0.1.20'
   gemini: 'scylladb/hydra-loaders:gemini-v1.8.6'
   alternator-dns: 'scylladb/hydra-loaders:alternator-dns-0.1'