test_cat: specify the reading size to read in binary mode (#4730)

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

test/command/test_cat.rb

@@ -87,7 +87,7 @@ def test_cat_secondary_file
       d = create_driver
       d.run(expect_records: 1) do
         Open3.pipeline_w("#{ServerEngine.ruby_bin_path} #{FLUENT_CAT_COMMAND} --port #{@port} --format msgpack secondary") do |stdin|
-          stdin.write(File.read(path))
+          stdin.write(File.read(path, File.size(path)))
           stdin.close
         end
       end