Fix warning about missing font when "cm" is not installed on the system

Use "cm" as preferred serif font, but keep the default serif fonts afterwards in the priority list.

replot/helpers/custom_mpl.py

@@ -3,6 +3,8 @@ Functions to set custom :mod:`matplotlib` parameters.
 """
 import shutil
 
+import matplotlib as mpl
+
 import numpy as np
 
 
@@ -26,7 +28,7 @@ def custom_rc(rc=None):
     # Use LaTeX default font family
     # See https://stackoverflow.com/questions/17958485/matplotlib-not-using-latex-font-while-text-usetex-true
     custom_rc_["font.family"] = "serif"
-    custom_rc_["font.serif"] = "cm"
+    custom_rc_["font.serif"] = ["cm"] + mpl.rcParams["font.serif"]
     # Scale everything
     custom_rc_.update(_rc_scaling())
     # Set axes style