Avoid passing None to arguments of prepare_shell_job_inputs

[GeigerJ2]

Originally noted in #348, and fixes #348.

The reason for the bug was that in this line:

aiida-workgraph/aiida_workgraph/engine/utils.py

Line 139 in 8f6260b

kwargs = {key: inputs.pop(key, None) for key in signature.parameters.keys()}

iteration was done over all input arguments of the prepare_shell_job_inputs function, using None as the default for the ones that weren't contained in the inputs dictionary passed to the prepare_for_shell_task function of WorkGraph. This would lead to None values being passed explicitly to the arguments of prepare_shell_job_inputs, in particular resolve_command, effectively overriding its default True value.

Inside aiida-shell the check for the absolute path of the executable inside the prepare_code function (see here) would thus be skipped, and the WorkGraph would just fail silently at a later stage. With this PR, only the input arguments that are also contained in the inputs of the prepare_for_shell_task are being explicitly passed, while the rest is left unset.

[superstar54]

LGTM! Please merge if all tests pass.