fix: environment handling windows (host mode) (#1732)

* fix: environment handling windows (host mode)

* fixup

* fixup

* add more tests

* fixup

* fix setenv

* fixes

* [skip ci] Apply suggestions from code review

Co-authored-by: Jason Song <i@wolfogre.com>

* Update side effects

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pkg/runner/testdata/windows-add-env/action.yml

@@ -0,0 +1,7 @@
+runs:
+  using: composite
+  steps:
+  - run: |
+      echo $env:GITHUB_ENV
+      echo "kEy=n/a" > $env:GITHUB_ENV
+    shell: pwsh