Remove R20 from github workflow

Author: prefiks

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        otp: [20, 25, 26, 27, 28, 29]
+        otp: [25, 26, 27, 28, 29]
     runs-on: ubuntu-24.04
     container:
       image: public.ecr.aws/docker/library/erlang:${{ matrix.otp }}