devel/py-unittest2: limit supported python versions
File "/wrkdirs/usr/ports/devel/py-unittest2/work-py310/unittest2-1.1.0/unittest2/compatibility.py", line 143, in <module> class ChainMap(collections.MutableMapping):
AttributeError: module 'collections' has no attribute 'MutableMapping'
Approved by: portmgr blanket