Update CI matrix

Author: kipcole9

.github/workflows/ci.yml

@@ -44,8 +44,10 @@ jobs:
             elixir: "1.17.2-otp-27"
           - otp: "27.2"
             elixir: "1.18.1-otp-27"
-          - otp: "28.3"
+          - otp: "28.3.1"
             elixir: "1.19.4-otp-28"
+          - otp: "28.3.1"
+            elixir: "1.20.0-rc.1-otp-28"
             lint: true
     steps:
     # Step: Setup Elixir + Erlang image as the base.