Add every path in XDG_DATA_DIRS to sage_data_paths.

Not just the first one.

Author: antonio-rojas

src/sage/env.py

@@ -536,8 +536,8 @@ def sage_data_paths(name: str | None) -> set[str]:
         }
         paths.add(user_data_dir("sagemath"))
         paths.add(user_data_dir())
-        paths.add(site_data_dir("sagemath"))
-        paths.add(site_data_dir())
+        for path in site_data_dir("sagemath", multipath=True).split(':') + site_data_dir(multipath=True).split(':'):
+            paths.add(path)
     else:
         paths = {path for path in SAGE_DATA_PATH.split(os.pathsep)}