chore: drop v20.04 (#253)

Author: DeepDiver1975

.github/workflows/main.yml

@@ -30,7 +30,6 @@ jobs:
         version:
           - value: "24.04"
           - value: "22.04"
-          - value: "20.04"
 
   update-docker-hub-description:
     needs: build

README.md

@@ -20,7 +20,6 @@ ownCloud Docker Ubuntu base image based on the [official Ubuntu](https://registr
 
 - [`24.04`](https://github.com/owncloud-docker/ubuntu/blob/master/v24.04/Dockerfile.multiarch) available as `owncloud/ubuntu:24.04`
 - [`22.04`](https://github.com/owncloud-docker/ubuntu/blob/master/v22.04/Dockerfile.multiarch) available as `owncloud/ubuntu:22.04`
-- [`20.04`](https://github.com/owncloud-docker/ubuntu/blob/master/v20.04/Dockerfile.multiarch) available as `owncloud/ubuntu:20.04`
 
 ## Default volumes