CI: Test with Erlang 28, remove 20

Author: badlop

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        otp: [20, 24, 25, 26, 27]
+        otp: [21, 24, 25, 26, 27, 28]
     runs-on: ubuntu-24.04
     container:
       image: erlang:${{ matrix.otp }}