fix flaky tsdb/30_snapshot.yaml spec (#84755)

Feature state indices are added to the snapshot implicitly even if they
are not listed int the indices field. This change is disabling 
features explicitly to avoid .tasks index in the snashpot.

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/snapshot.restore/10_basic.yml

@@ -34,6 +34,7 @@ setup:
         wait_for_completion: true
         body:
           indices: "test_index"
+          feature_states: ["none"]
 
   - match: { snapshot.snapshot: test_snapshot_1 }
   - match: { snapshot.state : SUCCESS }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/tsdb/30_snapshot.yml

@@ -102,7 +102,8 @@ teardown:
         snapshot: test_restore_tsdb
         wait_for_completion: true
         body:
-          indices: test_index
+          indices: "test_index"
+          feature_states: ["none"]
 
   - match: { snapshot.snapshot: test_restore_tsdb }
   - match: { snapshot.state : SUCCESS }