content: normalize github product variables in integrations/index.md

Refactored product name references within the integrations/index.md directory.
Replaced hardcoded strings and deprecated 'prodname_dotcom' variables
with the current standard '{% data variables.product.github %}' to align
with the GitHub Docs style guide and naming conventions.

Author: wd006

content/integrations/index.md

@@ -1,6 +1,6 @@
 ---
 title: GitHub integrations
-intro: 'Learn how to connect, extend, and customize GitHub with apps and tools.'
+intro: 'Learn how to connect, extend, and customize {% data variables.product.github %} with apps and tools.'
 shortTitle: Integrations
 layout: discovery-landing
 heroImage: /assets/images/banner-images/hero-2