fix: interpolate env for step actions (#872)

Signed-off-by: hackercat <me@hackerc.at>

pkg/runner/testdata/actions/docker-local/action.yml

@@ -11,5 +11,7 @@ outputs:
 runs:
   using: 'docker'
   image: 'Dockerfile'
+  env:
+    WHOAMI: ${{ inputs.who-to-greet }}
   args:
     - ${{ inputs.who-to-greet }}

pkg/runner/testdata/actions/docker-local/entrypoint.sh

@@ -3,5 +3,6 @@
 echo "Hello $1"
 time=$(date)
 echo ::set-output name=time::$time
+echo ::set-output name=whoami::$WHOAMI
 
 echo "SOMEVAR=$1" >>$GITHUB_ENV

pkg/runner/testdata/local-action-dockerfile/push.yml

@@ -7,10 +7,12 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - uses: ./actions/docker-local
+      id: dockerlocal
       with:
         who-to-greet: 'Mona the Octocat'
     - run: '[[ "${{ env.SOMEVAR }}" == "Mona the Octocat" ]]'
     - run: '[ "${SOMEVAR}" = "Not Mona" ] || exit 1'
       env:
         SOMEVAR: 'Not Mona'
+    - run: '[[ "${{ steps.dockerlocal.outputs.whoami }}" == "Mona the Octocat" ]]'
     - uses: ./localdockerimagetest_