config: Update some 'callers' of config.shutting_down for it being a property

dashboard.py

@@ -145,7 +145,7 @@ class Dashboard(FileSystemEventHandler):
 
     # Can be called either in watchdog thread or, if polling, in main thread.
     def process(self, logfile=None):
-        if config.shutting_down():
+        if config.shutting_down:
             return
 
         try:

hotkey.py

@@ -128,7 +128,7 @@ if platform == 'darwin':
             self.acquire_state = HotkeyMgr.ACQUIRE_INACTIVE
 
         def _acquire_poll(self):
-            if config.shutting_down():
+            if config.shutting_down:
                 return
 
             # No way of signalling to Tkinter from within the monkey-patched event handler that doesn't

plug.py

@@ -371,7 +371,7 @@ def show_error(err):
     :param err:
     .. versionadded:: 2.3.7
     """
-    if config.shutting_down():
+    if config.shutting_down:
         logger.info(f'Called during shutdown: "{str(err)}"')
         return