[ci] use ruby 2.6 in release step

Author: solnic

.github/workflows/ci.yml

@@ -71,7 +71,7 @@ jobs:
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 2.6
+          ruby-version: 3.0
       - name: Install dependencies
         run: gem install ossy --no-document
       - name: Trigger release workflow