Fix matplotlibrc path

gitlab/functions.sh

@@ -443,5 +443,5 @@ export_env LC_ALL
 
 # Set up the location of matplotlibrc:
 # https://matplotlib.org/users/customizing.html#the-matplotlibrc-file
-MATPLOTLIBRC="_ci"
+MATPLOTLIBRC="${CI_PROJECT_DIR}/_ci"
 export_env MATPLOTLIBRC

gitlab/recipe_append.yaml

 build:
   script_env:
     - DOCSERVER
-    - MATPLOTLIBRC