fix: composite action input pollution (#2348)

* fix: composite action input pollution

* fix run steps

* fix missing defaults in post after env cleanup

* fix test to make more sense

* Add tests and simplify change

---------

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

pkg/runner/testdata/uses-composite-check-for-input-collision/composite_action/action.yml

@@ -0,0 +1,16 @@
+name: "Test Composite Action"
+description: "Test action uses composite"
+
+inputs:
+  cache:
+    default: none
+
+runs:
+  using: "composite"
+  steps:
+  - uses: ./uses-composite-check-for-input-collision/action-with-pre-and-post
+    with:
+      step: step1
+  - uses: ./uses-composite-check-for-input-collision/action-with-pre-and-post
+    with:
+      step: step2