Rename 'downloader_suffix' to 'suffix'

his commit changes the variable name from 'downloader_suffix' to 'suffix' in the relevant test code. This helps avoid the implication that we are using more than one suffix in this test, which could lead to confusion. It also aligns the naming convention in this test with that in the production code, where 'suffix' is used in the same context.

test/onigumo_downloader_test.exs

@@ -117,8 +117,8 @@ defmodule OnigumoDownloaderTest do
       created_file_name = Onigumo.Downloader.create_file_name(input_url)
 
       input_url_hash = Onigumo.Utilities.Hash.md5(input_url, :hex)
-      downloaded_suffix = Application.get_env(:onigumo, :downloaded_suffix)
-      expected_file_name = input_url_hash <> downloaded_suffix
+      suffix = Application.get_env(:onigumo, :downloaded_suffix)
+      expected_file_name = input_url_hash <> suffix
 
       assert(created_file_name == expected_file_name)
     end