test Elixir master on OTP 24

Author: mkaput

.github/workflows/CI.yml

@@ -18,7 +18,7 @@ jobs:
         pair:
           - otp: "23"
             elixir: "1.10"
-          - otp: "23"
+          - otp: "24"
             elixir: "master"
 
     steps: