[mypy] Add/fix type annotations in `data_structures/heap/skew_heap.py` (#5634)
[mypy] Add/fix type annotations in `data_structures/heap/skew_heap.py` (#5634)

* Add abstract base class Comparable

* [mypy] Fix type annotations (strict mode)

* Fix a typo

* Remove Comparable class and set bound to bool
TheAlgorithms/Python