add OTP-28 to the CI matrix

Author: mikpe

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         platform: [ubuntu-latest]
-        otp-version: [25, 26, 27]
+        otp-version: [25, 26, 27, 28]
     runs-on: ${{ matrix.platform }}
     container:
       image: erlang:${{ matrix.otp-version }}