It depends on whether you're a warm or cold sleeper, what kind of accommodation you'll stay at, ect...
I've been cold some nights on the Francés even in july and was happy to have a warm down sleeping bag then. Others are happy with only a liner even in october.
During spring from Le Puy, you can still expect snow in the Aubrac. If you plan to stay in the cheaper gites you might be happy to have a good sleeping bag at least on some of the days. When you arrive cold and wet, the last thing you want is to freeze at night because you wanted to save 200g.
For what it's worth, on my first Camino in spring of 2015 I met a girl who had brought only a liner. Was cold each night, then bought a fleece blanket. Was still cold, then bought a sleeping bag and was happy.
I walked with a lightweight sleeping bag and some nights also used my heavy wool coat as an additional blanket and slept fully clothed and it was still a bit chilly for me. But that's just me.
You've already walked in spring, you should already have an idea what you personally need