Add literal/1 deprecation to changelog (#4620)

Co-authored-by: José Valim <jose.valim@dashbit.co>

Author: zachdaniel

CHANGELOG.md

@@ -34,6 +34,7 @@ Requires Elixir v1.14+.
 ### Soft deprecations (no warnings emitted)
 
   * [Ecto.Repo] `Ecto.Repo.transaction/2` is soft-deprecated in favor of `Ecto.Repo.transact/1`
+  * [Ecto.Query.API] `literal/1` is deprecated in favor of `identifier/1`
 
 ## v3.12.6 (2025-06-11)