Server error notification key

Summary: Add key for server error notifications as to prevent duplicates.

Reviewed By: antonk52

Differential Revision: D47869240

fbshipit-source-id: 7c826ab07a8f92bd053200786ed990ad78bbfa67

desktop/flipper-ui-core/src/dispatcher/flipperServer.tsx

@@ -53,9 +53,11 @@ export function connectFlipperServerToStore(
     if (err.code === 'EADDRINUSE') {
       handeEADDRINUSE('' + err);
     } else {
+      const text = err.message ?? err;
       notification.error({
+        key: text,
         message: 'Connection error',
-        description: <NotificationBody text={err.message ?? err} />,
+        description: <NotificationBody text={text} />,
         duration: null,
       });
     }