Add reason parameter to MergeGroupEvent (#3508)

Author: aguthrie

github/event_types.go

@@ -858,8 +858,10 @@ type MergeGroup struct {
 //
 // GitHub API docs: https://docs.github.com/developers/webhooks-and-events/webhook-events-and-payloads#merge_group
 type MergeGroupEvent struct {
-	// The action that was performed. Currently, can only be checks_requested.
+	// The action that was performed. Possible values are: "checks_requested", "destroyed".
 	Action *string `json:"action,omitempty"`
+	// Reason is populated when the action is "destroyed". Possible values: "merged", "invalidated", "dequeued".
+	Reason *string `json:"reason,omitempty"`
 	// The merge group.
 	MergeGroup *MergeGroup `json:"merge_group,omitempty"`
 

github/event_types_test.go

@@ -10746,6 +10746,7 @@ func TestMergeGroupEvent_Marshal(t *testing.T) {
 
 	u := &MergeGroupEvent{
 		Action: Ptr("a"),
+		Reason: Ptr("r"),
 		MergeGroup: &MergeGroup{
 			HeadSHA:    Ptr("hs"),
 			HeadRef:    Ptr("hr"),
@@ -10886,6 +10887,7 @@ func TestMergeGroupEvent_Marshal(t *testing.T) {
 
 	want := `{
 		"action": "a",
+		"reason": "r",
 		"merge_group": {
 			"head_sha": "hs",
 			"head_ref": "hr",