[Rollup] Update versions after backport

Both serialization and yaml test skips

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/rollup/action/StopRollupJobAction.java

@@ -79,8 +79,7 @@ public class StopRollupJobAction extends Action<StopRollupJobAction.Response> {
         public void readFrom(StreamInput in) throws IOException {
             super.readFrom(in);
             id = in.readString();
-            // TODO change this after backport
-            if (in.getVersion().onOrAfter(Version.CURRENT)) {
+            if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
                 waitForCompletion = in.readBoolean();
                 timeout = in.readTimeValue();
             }
@@ -90,8 +89,7 @@ public class StopRollupJobAction extends Action<StopRollupJobAction.Response> {
         public void writeTo(StreamOutput out) throws IOException {
             super.writeTo(out);
             out.writeString(id);
-            // TODO change this after backport
-            if (out.getVersion().onOrAfter(Version.CURRENT)) {
+            if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
                 out.writeBoolean(waitForCompletion);
                 out.writeTimeValue(timeout);
             }

x-pack/plugin/src/test/resources/rest-api-spec/test/rollup/stop_job.yml

@@ -87,7 +87,7 @@ setup:
 ---
 "Test wait_for_completion default timeout":
   - skip:
-      version: " - 6.6.0"
+      version: " - 6.5.99"
       reason: wait_for_completion option was added in 6.6
 
   - do:
@@ -108,7 +108,7 @@ setup:
 ---
 "Test wait_for_completion with custom timeout":
   - skip:
-      version: " - 6.6.0"
+      version: " - 6.5.99"
       reason: wait_for_completion option was added in 6.6
 
   - do: