CI: Lint with Ruby 3.1

We install latest Solidus during linting code
and this requires at least Ruby 3.1

Author: tvdeyen

.circleci/config.yml

@@ -33,7 +33,7 @@ jobs:
   lint-code:
     executor:
       name: solidusio_extensions/sqlite
-      ruby_version: "3.0"
+      ruby_version: "3.1"
     steps:
       - solidusio_extensions/lint-code