terraform/language-navigation: Fix incorrect version number (#872)

This is to correct version number displayed in the menu and in the
breadcrumbs.

https://developer.hashicorp.com/terraform/language/upgrade-guides

<img width="1476" height="248" alt="Screenshot 2025-08-27 at 8 42 27 AM"
src="https://github.com/user-attachments/assets/0e0327ac-61c3-4751-ac17-69e520701984"
/>


The automation script is also being fixed to avoid this in the future:
hashicorp/terraform-releases#200

Author: radeksimko

content/terraform/v1.13.x/data/language-nav-data.json

@@ -1109,7 +1109,7 @@
     ]
   },
   {
-    "title": "Upgrading to Terraform v1.12",
+    "title": "Upgrading to Terraform v1.13",
     "path": "upgrade-guides"
   },
   {