Include the environment in missing dep error message, closes #7331

Author: José Valim

lib/mix/lib/mix/tasks/format.ex

@@ -224,7 +224,7 @@ defmodule Mix.Tasks.Format do
       :error ->
         Mix.raise(
           "Unknown dependency #{inspect(dep)} given to :import_deps in the formatter configuration. " <>
-            "The dependency is not listed in your mix.exs file"
+            "The dependency is not listed in your mix.exs for environment #{inspect(Mix.env())}"
         )
     end
   end

lib/mix/test/mix/tasks/format_test.exs

@@ -239,7 +239,7 @@ defmodule Mix.Tasks.FormatTest do
 
       message =
         "Unknown dependency :nonexistent_dep given to :import_deps in the formatter configuration. " <>
-          "The dependency is not listed in your mix.exs file"
+          "The dependency is not listed in your mix.exs for environment :dev"
 
       assert_raise Mix.Error, message, fn -> Mix.Tasks.Format.run([]) end
     end