Merge `package:fake_async` (#2291)

- [x] Move and fix workflow files and badges in the README.md
- [x] Rev the version of the package, so that pub.dev points to the
correct site
- [x] Add a line to the changelog:
```
* Move to `dart-lang/test` monorepo.
```

- [x] Add the package to the top-level readme of the monorepo:
```
| [fake_async](pkgs/fake_async/) | Fake asynchronous events such as timers and microtasks for deterministic testing. | [![pub package](https://img.shields.io/pub/v/fake_async.svg)](https://pub.dev/packages/fake_async) |
```

- [ ] **Important!** Merge the PR with 'Create a merge commit' (enabling
then disabling the `Allow merge commits` admin setting)
- [ ] Update the auto-publishing settings on
https://pub.dev/packages/fake_async/admin
- [ ] Add the following text to
https://github.com/dart-lang/fake_async/:'

```
> [!IMPORTANT]  
> This repo has moved to https://github.com/dart-lang/test/tree/main/pkgs/fake_async
```

- [ ] Publish using the autopublish workflow
- [ ] Push tags to GitHub using `git tag --list 'fake_async*' | xargs
git push origin`
- [ ] Close open PRs in dart-lang/fake_async with the following message:

`Closing as the
[dart-lang/fake_async](https://github.com/dart-lang/fake_async)
repository is merged into the
[dart-lang/test](https://github.com/dart-lang/test) monorepo. Please
re-open this PR there!`
      
- [ ] Transfer issues by running `dart run
pkgs/repo_manage/bin/report.dart transfer-issues --source-repo
dart-lang/fake_async --target-repo dart-lang/test --add-label
package:fake_async --apply-changes`
- [ ] Archive https://github.com/dart-lang/fake_async/


---

- [x] I’ve reviewed the contributor guide and applied the relevant
portions to this PR.

<details>
  <summary>Contribution guidelines:</summary><br>

- See our [contributor
guide](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md)
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](https://dart.dev/guides/language/effective-dart) and use `dart
format`.
- Most changes should add an entry to the changelog and may need to [rev
the pubspec package
version](https://github.com/dart-lang/sdk/blob/main/docs/External-Package-Maintenance.md#making-a-change).
- Changes to packages require [corresponding
tests](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md#Testing).

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