Downgrade Cassandra version for CI

The cassandra tests were run on the latest version of Cassandra 4.1.0
and most probably the version contains some bugs as some tests were
flaky. This PR pins version 4.0.7 for creating a 3-node Cassandra
cluster, which solves the flakiness problem, however, the root cause of
the problem is still unknown.
Additionally, memory flags `HEAP_NEWSIZE=512M` and `MAX_HEAP_SIZE=2048M`
are added for each node creation as the GitHub Actions Linux virtual
machine has a RAM limit of 7GB.

test/cluster/cassandra/docker-compose.yml

@@ -10,7 +10,7 @@ networks:
         - subnet: 172.42.0.0/16
 services:
   cassandra1:
-    image: cassandra
+    image: cassandra:4.0.7
     healthcheck:
         test: ["CMD", "cqlsh", "-e", "describe keyspaces" ]
         interval: 5s
@@ -21,8 +21,10 @@ services:
         ipv4_address: 172.42.0.2
     environment:
       - CASSANDRA_BROADCAST_ADDRESS=172.42.0.2
+      - HEAP_NEWSIZE=512M
+      - MAX_HEAP_SIZE=2048M
   cassandra2:
-    image: cassandra
+    image: cassandra:4.0.7
     healthcheck:
         test: ["CMD", "cqlsh", "-e", "describe keyspaces" ]
         interval: 5s
@@ -34,11 +36,13 @@ services:
     environment:
       - CASSANDRA_BROADCAST_ADDRESS=172.42.0.3
       - CASSANDRA_SEEDS=172.42.0.2
+      - HEAP_NEWSIZE=512M
+      - MAX_HEAP_SIZE=2048M
     depends_on:
       cassandra1:
         condition: service_healthy
   cassandra3:
-    image: cassandra
+    image: cassandra:4.0.7
     healthcheck:
         test: ["CMD", "cqlsh", "-e", "describe keyspaces" ]
         interval: 5s
@@ -50,6 +54,8 @@ services:
     environment:
       - CASSANDRA_BROADCAST_ADDRESS=172.42.0.4
       - CASSANDRA_SEEDS=172.42.0.2,172.42.0.3
+      - HEAP_NEWSIZE=512M
+      - MAX_HEAP_SIZE=2048M
     depends_on:
       cassandra2:
         condition: service_healthy