Collaboration is a technically very complicated thing, as it is easy for people working simultaneously to make conflicting changes. Something like Git is probably a necessary tool to manage collaboration.
An alternative approach is to avoid multiple people working on the same Construct project. For example one person could be the game artist producing all the sprites and backgrounds, and another person could import that to Construct and build the project. Then you don't need to handle the possibility of conflicting changes in the same Construct project.