use open() as context manager (#9579)

* use open() as context manager

* add changelog frag

plugins/modules/redhat_subscription.py

@@ -308,9 +308,8 @@ class Rhsm(object):
             else:
                 cfg.set('main', 'enabled', '0')
 
-            fd = open(tmpfile, 'w+')
-            cfg.write(fd)
-            fd.close()
+            with open(tmpfile, 'w+') as fd:
+                cfg.write(fd)
             self.module.atomic_move(tmpfile, plugin_conf)
 
     def enable(self):