`labgrid_run_binary` duplicates prior actions

For certain types of dependency graphs the labgrid_run_binary rule duplicates actions that it depends on as inputs.

An example of such a graph is the following:

Here the PreProcess and PostProcess stages are run using Skylib's rub_binary rule whereas the Process stage is using labgrid_run_binary.

The problem we see is that the Process stage ends up running twice. Once for the exec config and once for the target config as illustrated in: