feat: add skipped status as step result (#950)

Github sets the outcome and conclusion to skipped
and this PR does the same during the pipeline run for
the StepResults in act.

Co-authored-by: Björn Brauer <bjoern.brauer@new-work.se>

Co-authored-by: Björn Brauer <bjoern.brauer@new-work.se>

pkg/model/step_result.go

@@ -7,11 +7,13 @@ type stepStatus int
 const (
 	StepStatusSuccess stepStatus = iota
 	StepStatusFailure
+	StepStatusSkipped
 )
 
 var stepStatusStrings = [...]string{
 	"success",
 	"failure",
+	"skipped",
 }
 
 func (s stepStatus) MarshalText() ([]byte, error) {