update to maintained fork of backoff

[mdujava]

original lib shows warnings in python3.14+
$HOME/.local/share/virtualenvs/3scale-tests-3BDQW4-4/lib/python3.14/site-packages/cached_property.py:27: DeprecationWarning: 'asyncio.iscoroutinefunction' is deprecated and slated for removal in Python 3.16; use inspect.iscoroutinefunction() instead
if asyncio.iscoroutinefunction(self.func):

[mdujava]

same change in 3scale-qe/3scale-api-python-crd#10 and 3scale-qe/3scale-api-python#175

[cathal-bailey]

When I ran this locally, I'm getting the same error from pytest-asyncio:

/Users/cathalbailey/.local/share/virtualenvs/3scale-tests-fresh-y5P9bm8c/lib/python3.14/site-packages/pytest_asyncio/plugin.py:155: DeprecationWarning: 'asyncio.iscoroutinefunction' is deprecated and slated for removal in Python 3.16; use inspect.iscoroutinefunction() instead

Should this be updated in the pipfile also? pytest-asyncio = ">=1.0.0" resolves warning.