fix empty line ending

Author: florence-bockting

docs/how-to-guides/cubic_spline.py

@@ -165,7 +165,7 @@ def plot_spline(spline, x, ax, label, gradient=False):  # noqa: D103
 # above in which the `harmonisee` spline differs
 # from the `diverge_from` spline due to varying shifts in the
 # intercept (`[0.0, -1.2, 1.2]`) and slope (`[1.0, 0.7, 1.4]`).
-# However, this time we consider 
+# However, this time we consider
 # harmonisation time (`=1.0`) > convergence time (`=-1.0`).
 
 # %%