Exit with error status code when plan preview failed

Signed-off-by: Takumaron <[email protected]>

tool/actions-plan-preview/main.go

@@ -102,14 +102,14 @@ func main() {
 
 	if event.PRClosed {
 		doComment(failureBadgeURL + "Unable to run plan-preview for a closed pull request.")
-		return
+		log.Fatal("failed to run plan-preview for a closed pull request")
 	}
 
 	// TODO: When PR opened, `Mergeable` is nil for calculation.
 	// Here it is not considered for now, but needs to be handled.
 	if event.PRMergeable != nil && *event.PRMergeable == false {
 		doComment(failureBadgeURL + "Unable to run plan-preview for an un-mergeable pull request. Please resolve the conficts and try again.")
-		return
+		log.Fatal("failed to run plan-preview for an un-mergeable pull request.")
 	}
 
 	result, err := retrievePlanPreview(
@@ -135,7 +135,7 @@ func main() {
 		}
 		if !pr.GetClosedAt().IsZero() {
 			doComment(failureBadgeURL + "Unable to run plan-preview for a closed pull request.")
-			return
+			log.Fatal("failed to run plan-preview for a closed pull request.")
 		}
 	}