Per this https://itnext.io/how-to-set-up-github-workflows-and-create-github-actions-using-docker-3a5ba7ec0988

  "A Docker-based action works in an isolated environment. When a step specifies such an action using uses field, a docker container is spawned using the Dockerfile of the action and *the Docker container takes the responsibility from there onwards.*"

idk, let's see if it stays in the docker container for subsequent steps

Author: maltfield

.github/workflows/build.yml

@@ -22,8 +22,12 @@ jobs:
         sudo lsmod
       shell: bash
 
+    - name: Enter a docker environment
+      uses: docker://debian:buster-slim
+
+    - uses: actions/checkout@v2
+
     - name: Execute script to build linux AppImage
-      container: debian:buster-slim
       run: "build/linux/buildAppImage.sh"
       shell: bash