when the H3 server closes the stream short of sending as much as that declared...

when the H3 server closes the stream short of sending as much as that declared in `content-length`, curl-ngtcp2 might not surface the partially delivered bytes; add wait to force it dto do so

t/50mruby-http-request.t

@@ -87,6 +87,7 @@ hosts:
                 end
                 def each(&b)
                   \@a.each(&b)
+                  sleep 0.1
                 end
               end
               body = T.new(body)
@@ -212,7 +213,6 @@ EOT
                 };
             };
             subtest "chunked" => sub {
-                local $TODO = "HTTP/3 is not yet supported" if $curl_cmd =~ /--http3/;
                 for my $i (0..30) {
                     subtest "cl=$i" => sub {
                         my ($headers, $body) = run_prog("$curl_cmd $proto://127.0.0.1:$port/cl/$i/chunked");