chore: update coverage to latest version

[alestiago]

Description

The current coverage version is pinned to 1.2.0, see: https://github.com/VeryGoodOpenSource/very_good_workflows/blob/b7d3a7d287a7ed1f996861a73d69eafdfd7ed60e/.github/workflows/dart_package.yml#L102

Currently, the latest coverage version is 1.6.3, see coverage's pub page. It would be ideal if the workflow used the latest version so the newest fixes apply.

I'm unaware of why the version is currently pinned, if the reason is stronger than the need to update then a valid solution would be to document this reasoning.

Additional Context

• Pull Request addressing this change
• Docs affected by this change