Update images, fix extrapath (#723)

* fix: typo

* fix: remove debug for git references

it generates a massive amount of logs

* feat: read values from env

allows to test act on GHA when it's not a main repo

* fix: merge extrapath with PATH

* fix(tests): add additional shells for testing

* fix(image): update images

pin node to major version only, current node version: 12.22.1
replace most images with `node:12-buster-slim` to prevent
errors on macOS runner due to DockerHub pull limit
replace ocaml image

Co-authored-by: Casey Lee <cplee@nektos.com>

pkg/runner/testdata/job-container-non-root/push.yml

@@ -4,7 +4,7 @@ on: push
 jobs:
   test:
     runs-on: ubuntu-latest
-    container: 
-      image: ocaml/opam2:debian-9-opam
+    container:
+      image: ghcr.io/catthehacker/ubuntu:runner-latest # image with user 'runner:runner' built on tag 'act-latest'
     steps:
       - run: echo PASS