chore: Run test matrix on Elixir 1.20.x

Author: crbelaus

.github/workflows/elixir.yml

@@ -28,6 +28,8 @@ jobs:
             erlang: "27.x"
           - elixir: "1.19.x"
             erlang: "28.x"
+          - elixir: "latest"
+            erlang: "28.x"
     services:
       db:
         image: postgres:15