Update CHANGELOG.md

Author: alisdair

CHANGELOG.md

@@ -11,6 +11,7 @@ ENHANCEMENTS:
 BUG FIXES:
 
 * Terraform now handles type constraints, nullability, and custom variable validation properly for root module variables. Previously there was an order of operations problem where the nullability and custom variable validation were checked too early, prior to dealing with the type constraints, and thus that logic could potentially "see" an incorrectly-typed value in spite of the type constraint, leading to incorrect errors. [GH-29959]
+* `terraform show -json`: JSON plan output now correctly maps aliased providers to their configurations, and includes the full provider source address alongside the short provider name. [GH-30138]
 
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