GitHub Action CI: Add Go source file format check (#6090)

https://github.com/XTLS/Xray-core/pull/6057#issuecomment-4364819830

And https://github.com/XTLS/Xray-core/pull/6149#issuecomment-4546876261

proxy/vless/validator.go

@@ -79,7 +79,7 @@ func (v *MemoryValidator) GetByEmail(email string) *protocol.MemoryUser {
 
 // Get all users
 func (v *MemoryValidator) GetAll() []*protocol.MemoryUser {
-	var u = make([]*protocol.MemoryUser, 0, 100)
+	u := make([]*protocol.MemoryUser, 0, 100)
 	v.email.Range(func(key, value interface{}) bool {
 		u = append(u, value.(*protocol.MemoryUser))
 		return true