Fix compatibility with Python 3.10
Fix compatibility with Python 3.10

Python 3.10 removed aliases to Collections Abstract Base Classes that
were deprecated in Python 3.3.

Fix this by just using collections.abc directly without using the alias.

https://docs.python.org/3.10/whatsnew/changelog.html#python-3-10-0-alpha-5

GNOME/orca,GNOME/orca,GNOME/orca,GNOME/orca