Process functions allow non-Data arguments to be passed as input

[sphuber]

MWE:

In [1]: from aiida import engine, orm

In [2]: @engine.calcfunction
   ...: def test_kwargs(**kwargs):
   ...:     for value in kwargs.values():
   ...:         assert isinstance(value, orm.Data)
   ...: 
   ...: 

In [3]: test_kwargs(**{'a': orm.Int(1)})
Out[3]: {}

In [4]: test_kwargs(**{'a': orm.Int(1), 'b': 1})
Report: [487|test_kwargs|on_except]: Traceback (most recent call last):
  File "/home/sph/.virtualenvs/aiida_dev/lib/python3.9/site-packages/plumpy/process_states.py", line 231, in execute
    result = self.run_fn(*self.args, **self.kwargs)
  File "/home/sph/code/aiida/env/dev/aiida-core/aiida/engine/processes/functions.py", line 395, in run
    result = self._func(*args, **kwargs)
  File "<ipython-input-2-5fb70fcb7652>", line 4, in test_kwargs
    assert isinstance(value, orm.Data)
AssertionError

As you can see, the second invocation of the test_kwargs calcfunction passes a normal int as an argument, but the input validation does not catch it and simply executes the function where the kwargs contains the normal int value. In contrast, if we don't use **kwargs but explicitly define the arguments, the validation does work:

In [5]: @engine.calcfunction
   ...: def test_explicit(a, b):
   ...:     assert isinstance(a, orm.Data)
   ...:     assert isinstance(b, orm.Data)

In [6]: test_explicit(a=orm.Int(1), b=5)

ValueError: Error occurred validating port 'inputs.b': value 'b' is not of the right type. Got '<class 'int'>', expected '(<class 'aiida.orm.nodes.data.data.Data'>,)'

Originally reported on the mailing list: https://groups.google.com/g/aiidausers/c/BmDOzte4vWQ/m/v7PZUTywBAAJ