fix: unclosed file <_io.BufferedReader name error by proper cleanup of subprocess.Popen process (#965)

#962
add a Popen.communicate call after terminate to ensure that file stdout and sdterr file descriptors are closed properly.

Author: WrrngnCode

appium/webdriver/appium_service.py

@@ -235,6 +235,7 @@ def stop(self) -> bool:
         if self.is_running:
             assert self._process
             self._process.terminate()
+            self._process.communicate(timeout=5)
             is_terminated = True
         self._process = None
         self._cmd = None