[ci] Add ruby-3.1.0-preview1

Author: flash-gordon

.github/workflows/ci.yml

@@ -25,6 +25,7 @@ jobs:
       fail-fast: false
       matrix:
         ruby:
+        - "3.1.0-preview1"
         - "3.0"
         - "2.7"
         - "2.6"