It's not that easy. First, who are the centrist? Things shifted to the right so much Macron is definitely right wing. You might call the Parti Socialiste (PS) centrist, it has a right and left wing in itself. In this sense you can call it an alliance.
But if you are talking about Macron's party I wouldn't call that an alliance. Some withdrew when they were against a far right and a PS opponent but some didn't when it was against a far right and a leftist opponent (or they had to be heavily pressured). And now in the parliament it's definitely not going to be an alliance, they'll be voting against most things the Nouveau Front Populaire (NFP) brings up, they voted with the far right in the past and will do it again.
The whole point of Macron's dissolution was probably to break the left in the first place, and they keep trying to split the NFP by saying they are willing to negotiate with it's center part but not it's left part.