Support rails 8

https://github.com/rameerez/dashboards/blob/main/dashboards.gemspec#L36

```
Could not find compatible versions

Because every version of dashboards depends on rails >= 7.0, < 8.A
  and Gemfile depends on rails ~> 8.0.0,
  dashboards cannot be used.
So, because Gemfile depends on dashboards >= 0,
  version solving has failed.

```