fix: rewrite StepContext env (#832)

* fix: rewrite StepContext env

step env from workflow should be last one to be written
fixes https://github.com/nektos/act/issues/777

* test: verify env correctness

* fix: move test into existing workflow

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

@@ -10,4 +10,7 @@ jobs:
       with:
         who-to-greet: 'Mona the Octocat'
     - run: '[[ "${{ env.SOMEVAR }}" == "Mona the Octocat" ]]'
+    - run: '[ "${SOMEVAR}" = "Not Mona" ] || exit 1'
+      env:
+        SOMEVAR: 'Not Mona'
     - uses: ./localdockerimagetest_