Replace deprecated setup-ruby action

The following error was being encountered in https://github.com/DMPRoadmap/roadmap/actions/runs/13907418160/job/38913596385?pr=3487:

```
Run actions/setup-ruby@v1
------------------------
NOTE: This action is deprecated and is no longer maintained.
Please, migrate to https://github.com/ruby/setup-ruby, which is being actively maintained.
------------------------
Error: Version 3.0.4 not found
```

Author: aaronskiba

.github/workflows/danger.yml

@@ -16,7 +16,7 @@ jobs:
 
     # Install Ruby - using the version found in the Gemfile.lock
     - name: 'Install Ruby'
-      uses: actions/setup-ruby@v1
+      uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ env.RUBY_VERSION }}