fix: material_maps:allow_failure:true since using compiled code instead of python3

The reference implementation of material maps is at https://acts.readthedocs.io/en/latest/examples/howto/material_mapping.html and uses the python3 interfaces. The compiled C++ interfaces are unmaintained and do not work anymore in recent versions of Acts.

benchmarks/material_maps/config.yml

@@ -20,3 +20,4 @@ material_maps:
   artifacts:
     paths:
       - results/material_maps
+  allow_failure: true