Fix filepath in toc

Author: anandmeg

docs/toc.yml

@@ -158,7 +158,7 @@
     - name: Copilot Edits
       href: ide/copilot-edits.md
     - name: Custom models in chat
-      href: ide/copilot-add-custom-models.md
+      href: ide/copilot-add-custom-model.md
   - name: Chat context
     items:
     - name: Customize responses