Fix typo

StackOverflow -> Stack Overflow

Author: changeworld

articles/azure-signalr/TOC.yml

@@ -227,7 +227,7 @@
     href: https://azure.microsoft.com/pricing/details/signalr-service/
   - name: Videos
     href: https://www.youtube.com/results?search_query=Azure+SignalR+Core
-  - name: StackOverflow
+  - name: Stack Overflow
     href: https://stackoverflow.com/search?q=signalr+service
   - name: X
     href: https://x.com/SignalR