fixed formatting of variable in json

Author: Supplementing

x-pack/plugin/core/template-resources/src/main/resources/fleet-integration-knowledge.json

@@ -8,7 +8,7 @@
       "dynamic": false,
       "_meta": {
         "version": "${fleet.version}",
-        "managed_index_mappings_version": "${fleet.managed.index.version}",
+        "managed_index_mappings_version": ${fleet.managed.index.version},
         "description": "Integration package knowledge base content storage",
         "managed": true
       },