chore: bump contentctl.yml and build.yml to 6.4.0

Author: research bot

build.yml

@@ -9,7 +9,7 @@ author: Splunk Threat Research Team
 author_email: research@splunk.com
 content_prefix: ESCU
 label: ES Content Updates
-app_version: 6.3.0
+app_version: 6.4.0
 description: Explore the Analytic Stories included with ES Content Updates.
 id: DA-ESS-ContentUpdate
 external_app_content:

contentctl.yml

@@ -3,7 +3,7 @@ app:
   uid: 3449
   title: ES Content Updates
   appid: DA-ESS-ContentUpdate
-  version: 6.3.0
+  version: 6.4.0
   description: Explore the Analytic Stories included with ES Content Updates.
   prefix: ESCU
   label: ESCU