build: do not use cached snapshots for backwards compatibility tests

The backwards compatibility tests rely on gradle's built-in mechanisms for resolving dependencies
to get the zip of the older version we test against. By default, this will cache snapshots for
24 hours, which can lead to unexpected failures in CI. This change makes the special configurations
for backwards compatibility always update their snapshots by setting the amount of time to cache
to 0 seconds.

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy

@@ -39,6 +39,7 @@ import org.gradle.api.tasks.Delete
 import org.gradle.api.tasks.Exec
 
 import java.nio.file.Paths
+import java.util.concurrent.TimeUnit
 
 /**
  * A helper for creating tasks to build a cluster that is used by a task, and tear down the cluster when the task is finished.
@@ -91,6 +92,8 @@ class ClusterFormationTasks {
                 configureBwcPluginDependency("${task.name}_elasticsearchBwcPlugins", project, entry.getValue(),
                         project.configurations.elasticsearchBwcPlugins, config.bwcVersion)
             }
+            project.configurations.elasticsearchBwcDistro.resolutionStrategy.cacheChangingModulesFor(0, TimeUnit.SECONDS)
+            project.configurations.elasticsearchBwcPlugins.resolutionStrategy.cacheChangingModulesFor(0, TimeUnit.SECONDS)
         }
         for (int i = 0; i < config.numNodes; i++) {
             // we start N nodes and out of these N nodes there might be M bwc nodes.