fix: typo in System Design roadmap (#7953)

src/data/roadmaps/system-design/system-design.json

@@ -5083,7 +5083,7 @@
       },
       "selected": false,
       "data": {
-        "label": "Backens for Frontend",
+        "label": "Backends for Frontend",
         "style": {
           "fontSize": 17,
           "justifyContent": "flex-start",
@@ -7119,4 +7119,4 @@
       "focusable": true
     }
   ]
-}
+}