isort-py is old and fails being used on py310

[nieder]

From a pymod I'm packaging that uses isort-py:

    import isort.api
  File "/sw/lib/python3.10/site-packages/isort/__init__.py", line 25, in <module>
    from . import settings  # noqa: F401
  File "/sw/lib/python3.10/site-packages/isort/settings.py", line 34, in <module>
    from .pie_slice import itemsview, lru_cache, native_str
  File "/sw/lib/python3.10/site-packages/isort/pie_slice.py", line 362, in <module>
    class OrderedSet(collections.MutableSet):
AttributeError: module 'collections' has no attribute 'MutableSet'

MutableSet is now in collections.abc
https://www.datasciencelearner.com/python-exceptions/attributeerror/attributeerror-module-collections-has-no-attribute-mutablemapping/

This was fixed in upstream isort a while ago:
PyCQA/isort#756

Our isort 4.3.4is old, from early 2018. Barring dependencies, should be able to upgrade to 4.3.21 for py27-py36, 5.11.5 for py37, and 5.13.2 for py38+

[nieder]

I've pushed the MutableSet fix from upstream so that isort-py310 actually works now. Leaving this open to deal with upgrading isort.