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/shells/python/push.yml

@@ -0,0 +1,9 @@
+on: push
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - shell: python
+        run: |
+          import platform
+          print(platform.python_version())