is_valid_cache settter is broken for ProcessNodes

[ltalirz]

Describe the bug

7cea5be introduced an is_valid_cache setter that, in theory, can be used to invalidate specific process node instances as far as the cache is concerned:

n=load_node(<PK>)
n.base.caching.is_valid_cache = False

Unfortunately, the setter does not actually work on any ProcessNode

In [5]: n.base.caching.is_valid_cache=False
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-5-e4b12fc7cfcc> in <cell line: 1>()
----> 1 n.base.caching.is_valid_cache=False

/ohome/shared/a-ctalirz/aiida2/aiida-core/aiida/orm/nodes/process/process.py in is_valid_cache(self, valid)
     66         :param valid: whether the node is valid or invalid for use in caching.
     67         """
---> 68         super().is_valid_cache = valid  # type: ignore[misc]
     69 
     70     def _get_objects_to_hash(self) -> List[Any]:

AttributeError: 'super' object has no attribute 'is_valid_cache'

The reason is a programming error related to the fact that in Python super() cannot be used to access setters directly (see e.g. this StackOverflow post and links therein).

I'll prepare a PR