test: fix agent policy test to use Set assertion instead of List index

Update TestAccResourceAgentPolicy to use TestCheckTypeSetElemAttr instead
of index-based assertion for space_ids. Sets don't guarantee element order,
so index-based checks (space_ids.0) are incorrect. This brings the test
in line with the Set migration and matches the pattern used in
TestAccResourceAgentPolicySpaceReordering.

Author: jamesagarside

internal/fleet/agent_policy/acc_test.go

@@ -297,7 +297,7 @@ func TestAccResourceAgentPolicyWithSpaceIds(t *testing.T) {
 					resource.TestCheckResourceAttr("elasticstack_fleet_agent_policy.test_policy", "namespace", "default"),
 					resource.TestCheckResourceAttr("elasticstack_fleet_agent_policy.test_policy", "description", "Test Agent Policy with Space IDs"),
 					resource.TestCheckResourceAttr("elasticstack_fleet_agent_policy.test_policy", "space_ids.#", "1"),
-					resource.TestCheckResourceAttr("elasticstack_fleet_agent_policy.test_policy", "space_ids.0", "default"),
+					resource.TestCheckTypeSetElemAttr("elasticstack_fleet_agent_policy.test_policy", "space_ids.*", "default"),
 				),
 			},
 		},