Reorder content-disposition in multi file

[lwj1994]

resort content-type plz. to fix uplaod file error

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[brianquinlan]

Could you explain what your issue is and how this PR fixes it?

[github-actions]

PR Health

License Headers ✔️

// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/http/example/main.dart
pkgs/http_multi_server/test/cert.dart

This check can be disabled by tagging the PR with skip-license-check.

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbol	Leaking sources

This check can be disabled by tagging the PR with skip-leaking-check.

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
http	None	1.6.0	1.6.0	1.6.0	✔️

This check can be disabled by tagging the PR with skip-breaking-check.

Coverage ✔️

File	Coverage
pkgs/http/lib/src/multipart_request.dart	💚 93 % ⬆️ 0 %

This check for test coverage is informational (issues shown here will not fail the PR).

This check can be disabled by tagging the PR with skip-coverage-check.

Changelog Entry ❗

Package	Changed Files
package:http	pkgs/http/lib/src/multipart_request.dart

Changes to files need to be accounted for in their respective changelogs.

This check can be disabled by tagging the PR with skip-changelog-check.