Add OTP version '28.1-slim' to CI matrix

Author: andreineculau

.github/workflows/ci.yml

@@ -19,6 +19,7 @@ jobs:
       matrix:
         otp_vsn:
           - 'slim'
+          - '28.1-slim'
           - '28-slim'
           - '27.3-slim'
           # - '27.2-slim'