Fix p0=deprecation/10_basic/Test Deprecations (elastic#125687)

In elastic#120505 we introduced a capabilities check in the yaml test `deprecation/10_basic/Test Deprecations` but we forgot to add them in the `RestDeprecationInfoAction`.

In this PR we add the capabilities which will enable the test and we make the test resilient to the warning that occurs when the `.security-7` index is present.

Author: gmarouli

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/RestDeprecationInfoAction.java

@@ -16,11 +16,14 @@
 
 import java.io.IOException;
 import java.util.List;
+import java.util.Set;
 
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestDeprecationInfoAction extends BaseRestHandler {
 
+    private static final Set<String> SUPPORTED_CAPABILITIES = Set.of("data_streams", "ilm_policies", "templates");
+
     @Override
     public List<Route> routes() {
         return List.of(new Route(GET, "/_migration/deprecations"), new Route(GET, "/{index}/_migration/deprecations"));
@@ -47,4 +50,9 @@ private static RestChannelConsumer handleGet(final RestRequest request, NodeClie
         );
         return channel -> client.execute(DeprecationInfoAction.INSTANCE, infoRequest, new RestToXContentListener<>(channel));
     }
+
+    @Override
+    public Set<String> supportedCapabilities() {
+        return SUPPORTED_CAPABILITIES;
+    }
 }

x-pack/plugin/src/yamlRestTest/resources/rest-api-spec/test/deprecation/10_basic.yml

@@ -11,9 +11,11 @@ setup:
         - method: GET
           path: /_migration/deprecations
           capabilities: [ data_streams, ilm_policies, templates ]
-      test_runner_features: capabilities
+      test_runner_features: [capabilities, allowed_warnings]
       reason: "Support for data streams, ILM policies and templates"
   - do:
+      allowed_warnings:
+        - "this request accesses system indices: [.security-7], but in a future major version, direct access to system indices will be prevented by default"
       migration.deprecations:
         index: "*"
   - length: { cluster_settings: 0 }