message: fix(chart-api): cached-indicator always shows value is cached
diff: @@ -282,7 +282,7 @@ class QueryContext:
  "cache_timeout": self.cache_timeout,
  "df": df,
  "error": error_message,
  - "is_cached": cache_key is not None,
  + "is_cached": cache_value is not None,
  "query": query,
  "status": status,
  "stacktrace": stacktrace,
  