Ensure locales have unique names

Previously, we listed both en-IN as "English (UK)" and es-MX as
"Castellano (ES)".

This commit adds a spec to ensure that the locales have a unique names
and updates the two offending locales.

config/locales/en-IN.yml

@@ -631,7 +631,7 @@ en-IN:
       available_locales:
       language:
       localization_settings:
-      this_file_language: English (UK)
+      this_file_language: English (IN)
     icon: Icon
     identifier:
     image: Image

config/locales/es-MX.yml

@@ -636,7 +636,7 @@ es-MX:
       available_locales: Traduciones Disponibles
       language: Idioma
       localization_settings: Ajustes de traducciones
-      this_file_language:
+      this_file_language: Castellano (MX)
     icon: Icono
     identifier:
     image: Imagen

spec/helpers/locale_helper_spec.rb

@@ -23,5 +23,13 @@
         is_expected.to match_array SolidusI18n::Locale.all
       end
     end
+
+    describe 'locale presentation' do
+      subject { all_locales_options.map(&:first) }
+
+      it 'should all be unique' do
+        is_expected.to match_array(subject.uniq)
+      end
+    end
   end
 end