Update docs workflow to use Ruby 3.2

Required for compatibility with newer gem versions from graphing-library-docs.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cpsievert

.github/workflows/docs.yml

@@ -46,7 +46,7 @@ jobs:
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: '2.7.4'
+          ruby-version: '3.2'
           bundler-cache: true
 
       - name: Fetch R/ggplot2 docs from plotly.r-docs