Update copilot-instructions.md (#62129)

Author: captainsafia

.github/copilot-instructions.md

@@ -4,6 +4,7 @@
 * Always use the latest version C#, currently C# 13 features.
 * Never change global.json unless explicitly asked to.
 * Never change package.json or package-lock.json files unless explicitly asked to.
+* Never change NuGet.config files unless explicitly asked to.
 
 ## Formatting