Don't use 'accept-encoding' in HttpIO requests

Net::HTTP does not automatically decompress requests sent with a
range header, as is done by HttpIO#request, causing the body of
any gzipped responses to be unreadable.

This change removes the 'accept-encoding' header from requests sent
by HttpIO, ensuring responses are not gzipped.

changelogs/unreleased/wc-httio-accept-encoding.yml

+---
+title: Don't send 'accept-encoding' in HttpIO requests
+merge_request: 28239
+author:
+type: fixed

lib/gitlab/http_io.rb

@@ -176,7 +176,7 @@ module Gitlab
     end
 
     def request
-      Net::HTTP::Get.new(uri).tap do |request|
+      Net::HTTP::Get.new(uri, { 'accept-encoding' => nil }).tap do |request|
         request.set_range(chunk_start, BUFFER_SIZE)
       end
     end

spec/lib/gitlab/http_io_spec.rb

@@ -319,4 +319,12 @@ describe Gitlab::HttpIO do
 
     it { is_expected.to be_truthy }
   end
+
+  describe '#send' do
+    subject(:send) { http_io.send(:request) }
+
+    it 'does not set the "accept-encoding" header' do
+      expect(send['accept-encoding']).to be_nil
+    end
+  end
 end