Append to List in Project Variables loads a stored list, adds the supplied
values to its end, and saves the result under the same key. If the key does not
exist, the action starts with an empty list.
The action has no output. Use Get Project Variable afterward when the
updated list is needed in the workflow.
The existing value must be a list. The action fails with Value is not a list
for another type, or Variable is corrupted when the stored value cannot be
read.
The value is shared by every workflow in the project. Simultaneous
read-and-append operations can overwrite one another, so this action is not a
transactional queue.
