broken link parsing with GitHubWeb extension

[isoos]

Version: 7.1.1
Originally reported on: dart-lang/pub-dev#7096

Source:

[Pub Package: https://pub.dev/packages/simple_architecture](https://pub.dev/packages/simple_architecture)

Using the GitHubWeb extension, it renders to:

<p>[Pub Package: <a href="https://pub.dev/packages/simple_architecture%5D(https://pub.dev/packages/simple_architecture)">https://pub.dev/packages/simple_architecture](https://pub.dev/packages/simple_architecture)</a></p>

Using it without the extension it renders correctly to:

<p><a href="https://pub.dev/packages/simple_architecture">Pub Package: https://pub.dev/packages/simple_architecture</a></p>

[lrhn]

The GitHub flavored markdown extension converts embedded valid URLs to links. It should probably not do that inside another link.