Require >=Ruby32

.github/actions/prepare-env/action.yml

@@ -6,7 +6,7 @@ runs:
   - name: Setup Ruby
     uses: ruby/setup-ruby@v1
     with:
-      ruby-version: 3.1
+      ruby-version: 3.3
   - name: Setup NodeJS
     uses: actions/setup-node@v2
     with:

README.md

@@ -13,7 +13,7 @@ a web server such as nginx, apache, etc.
 The following languages and tools have to be
 installed to build the website from source:
 
-* Ruby 3.1 (or later)
+* Ruby 3.2 (or later)
 * NodeJS v18.15 (or later)
 * [tidy-html5](https://github.com/htacg/tidy-html5)