🩹Fix for when the backsweep is a parameter rather than constant (glot…

…aran#1422)

* Fix for crashing optimizer when the backsweep is a parameter rather than constant

---------

Co-authored-by: s-weigand <s.weigand.phy@gmail.com>

glotaran/builtin/items/activation/gaussian.py

@@ -171,15 +171,15 @@ def parameters(
 
         scales = self.scale or [1.0] * nr_gaussians
         backsweep = self.backsweep is not None
-        backsweep_period = self.backsweep if backsweep else 0
+        backsweep_period = float(self.backsweep) if self.backsweep is not None else 0
 
         parameters: list[GaussianActivationParameters] = [
             GaussianActivationParameters(
                 float(center),
                 float(width),
                 float(scale),
                 backsweep,
-                backsweep_period,  # type:ignore[arg-type]
+                backsweep_period,
             )
             for center, width, scale in zip(centers, widths, scales)
         ]