do not forget the filename in those multipart spoofs

lib/httpx/plugins/multipart/part.rb

@@ -26,7 +26,7 @@ module HTTPX
           content_type ||= MimeTypeDetector.call(value, filename) || "application/octet-stream"
           [value, content_type, filename]
         else
-          [StringIO.new(value.to_s), content_type || "text/plain"]
+          [StringIO.new(value.to_s), content_type || "text/plain", filename]
         end
       end
     end

sig/plugins/multipart.rbs

@@ -33,7 +33,7 @@ module HTTPX
       end
 
       module Part
-        def self?.call: (multipart_nested_value) -> ([_Reader, String, String?] | [_Reader, String])
+        def self?.call: (multipart_nested_value) -> ([_Reader, String, String?])
       end
 
       module MimeTypeDetector

test/support/requests/plugins/multipart.rb

@@ -174,7 +174,7 @@ module Requests
           body = json_body(response)
           verify_header(body["headers"], "Content-Type", "multipart/form-data")
           # httpbin accepts the spoofed part, but it wipes our the content-type header
-          verify_uploaded(body, "form", "image" => "spoofpeg")
+          verify_uploaded_image(body, "image", "spoofpeg", skip_verify_data: true)
         end
       end
 
@@ -209,10 +209,12 @@ module Requests
         File.join("test", "support", "fixtures", fixture_file_name)
       end
 
-      def verify_uploaded_image(body, key, mime_type)
+      def verify_uploaded_image(body, key, mime_type, skip_verify_data: false)
         assert body.key?("files"), "there were no files uploaded"
         assert body["files"].key?(key), "there is no image in the file"
         # checking mime-type is a bit leaky, as httpbin displays the base64-encoded data
+        return if skip_verify_data
+
         assert body["files"][key].start_with?("data:#{mime_type}"), "data was wrongly encoded (#{body["files"][key][0..64]})"
       end
     end