Validate Content-Type value set by set_content_type

set_content_type assigned to @Header directly, bypassing the CR/LF
validation in set_field, so a crafted media type or parameter could
inject header lines.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hsbt

lib/net/http/header.rb

@@ -782,7 +782,7 @@ def type_params
   #
   # Net::HTTPHeader#content_type= is an alias for Net::HTTPHeader#set_content_type.
   def set_content_type(type, params = {})
-    @header['content-type'] = [type + params.map{|k,v|"; #{k}=#{v}"}.join('')]
+    set_field('Content-Type', type + params.map{|k,v|"; #{k}=#{v}"}.join(''))
   end
 
   alias content_type= set_content_type

test/net/http/test_httpheader.rb

@@ -451,6 +451,11 @@ def test_type_params
   end
 
   def test_set_content_type
+    @c.set_content_type 'text/html', {'charset' => 'utf-8'}
+    assert_equal 'text/html; charset=utf-8', @c['content-type']
+    assert_raise(ArgumentError){ @c.set_content_type "text/html\r\nFoo: bar" }
+    assert_raise(ArgumentError){ @c.set_content_type 'text/html', {'charset' => "x\r\nFoo: bar"} }
+    assert_raise(ArgumentError){ @c.set_content_type 'text/html', {"x\nFoo: bar" => 'utf-8'} }
   end
 
   def test_form_data=