text: Title: KEEP_ALIVE doesn't work from the 21.3 sanic version
  Body: ### Is there an existing issue for this?
  
  - [X] I have searched the existing issues
  
  ### Describe the bug
  
  When you put in the sanic config keep_alive to false, it doesn't work you can see in all responses "Connection": "keep-alive".
  
  I tryed with version 20.12.7 and sanic works correctly but in the version 21.3.0 it doesn't works
  
  ### Code snippet
  
  ```python
  import asyncio
  
  
  import uvloop
  from sanic import Sanic
  from sanic.response import text
  
  asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
  loop = asyncio.get_event_loop()
  app = Sanic('appname')
  
  
  @app.get('/status')
  async def status_handler(request):
      return text("", status=200)
  
  
  def main():
      app.config.KEEP_ALIVE = False
      server = app.run(host='0.0.0.0', port=8000)
      asyncio.run(server, loop=loop)
  
  
  if __name__ == '__main__':
      main()
  ```
  
  ### Expected Behavior
  
  I expect that the header "connection" of the response should be close if you put the config of KEEP_ALIVE=false
  
  ### How do you run Sanic?
  
  As a script (`app.run` or `Sanic.serve`)
  
  ### Operating System
  
  Linux
  
  ### Sanic Version
  
  >=21.3.0
  
  ### Additional context
  
  _No response_