Update PR Health install instructions

[mosuem]

As per the comments in dart-lang/test#2266.

Thanks @jakemac53 !

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

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[github-actions]

PR Health

Breaking changes ✔️

Details

Package	Change	Current Version	New Version	Needed Version	Looking good?
firehose	None	0.9.1	0.9.1	0.9.1	✔️

Coverage ✔️

Details

File	Coverage

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

API leaks ✔️

Details

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 symbols

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	3.2.0	already published at pub.dev
package:firehose	0.9.1	already published at pub.dev

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