Switch to interface{} instead of map[string]... (#700)

* fix: change `env` to be an interface

allows to use GitHub functions like `fromJson()`

* fix: change matrix to an interface instead of map

This allows to use GitHub functions like `fromJson()` to create dynamic
matrixes

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

pkg/runner/run_context.go

@@ -55,7 +55,7 @@ type stepResult struct {
 // GetEnv returns the env for the context
 func (rc *RunContext) GetEnv() map[string]string {
 	if rc.Env == nil {
-		rc.Env = mergeMaps(rc.Config.Env, rc.Run.Workflow.Env, rc.Run.Job().Env)
+		rc.Env = mergeMaps(rc.Config.Env, rc.Run.Workflow.Env, rc.Run.Job().Environment())
 	}
 	rc.Env["ACT"] = "true"
 	return rc.Env