Fix CI: specify ruby-version in setup-ruby, keep mise for local dev

Author: hschne

.github/workflows/jekyll.yml

@@ -20,11 +20,10 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
-      - name: Install mise
-        uses: jdx/mise-action@v2
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
         with:
+          ruby-version: "3.4.9"
           bundler-cache: true
       - name: Setup Pages
         id: pages