Refine Ruby version handling and workflow clarity

This commit introduces the following changes:

- Removes comments from the HTMLProofer GitHub Actions workflow file for conciseness.
- Adds a `.ruby-version` file specifying Ruby 3.0.0 for consistent Ruby versioning across environments.
- Updates the GitHub Actions workflow (`ruby/setup-ruby` step) to automatically use the Ruby version defined in the `.ruby-version` file, removing the explicit version setting.

These changes improve the clarity of the workflow and ensure consistent Ruby version management.

Author: google-labs-jules[bot]

.github/workflows/html-proofer.yml

@@ -0,0 +1,30 @@
+name: HTMLProofer
+
+on:
+  pull_request:
+
+jobs:
+  proof:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true # Runs bundle install and caches gems
+
+      - name: Cache HTMLProofer results
+        uses: actions/cache@v3
+        with:
+          path: tmp/.htmlproofer
+          key: ${{ runner.os }}-htmlproofer-${{ github.head_ref || github.run_id }}
+          restore-keys: |
+            ${{ runner.os }}-htmlproofer-
+
+      - name: Build Jekyll site
+        run: bundle exec jekyll build
+
+      - name: Run HTMLProofer
+        run: htmlproofer ./_site --allow-hash-href

.ruby-version

@@ -0,0 +1 @@
+3.0.0

Gemfile

@@ -1,6 +1,7 @@
 source 'https://rubygems.org'
 
 gem 'jekyll', '4.3.1'
+gem 'html-proofer'
 
 group :jekyll_plugins do
   gem 'jekyll-archives'