52ab9bbee9 makes a failure.
```
1) Failure:
HTTPRequestTest#test_initialize_HEAD [/tmp/ruby/v3/src/trunk/test/net/http/test_http_request.rb:53]:
<{"accept"=>["*/*"], "user-agent"=>["Ruby"]}> expected but was
<{"accept-encoding"=>["gzip;q=1.0,deflate;q=0.6,identity;q=0.3"],
"accept"=>["*/*"],
"user-agent"=>["Ruby"]}>.
```
I'm not sure it is correct, so please review later.
