Inconsistent shortest_path warning and return type on main

[eriknw]

Current Behavior

#7161 updated the warning for shortest_path to indicate the return type (from dict to iterator) will occur in NetworkX 3.5.

#6584 changed the return type from dict to iterator, but #7161 didn't change the return type back to dict.

Expected Behavior

I expect shortest_path with no source or target to return an iterator over node, path pairs on main branch to be consistent with the warning.

Steps to Reproduce

>>> import networkx as nx
>>> assert isinstance(nx.shortest_path(nx.complete_graph(4)), dict)  # raises AssertionError

Environment

Python version: 3.10
NetworkX version: main branch

Additional context

This is similar to issue #7315. I haven't fully compared #6584, #7161, and main branch to ensure consistency.