Checkout submodules for auto-publishing

[mosuem]

To avoid errors like https://github.com/dart-lang/i18n/actions/runs/7754336628.

---

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Contributions to our repos should follow the Dart style guide and use dart format.
• Most changes should add an entry to the changelog and may need to rev the pubspec package version.
• Changes to packages require corresponding tests.

Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.

[github-actions]

PR Health

Breaking changes ✔️

Details

Package	Change	Current Version	New Version	Needed Version	Looking good?

Changelog Entry ✔️

Details

Package	Changed Files

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

Coverage ✔️

Details

File	Coverage

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

License Headers ✔️

Details

// Copyright (c) 2024, 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.

Package publish validation ✔️

Details

Package	Version	Status
package:dart_flutter_team_lints	2.1.1	already published at pub.dev
package:firehose	0.6.1	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.