Fix deprecation warning in ibex_config.py
Fix deprecation warning in ibex_config.py

Fix a deprecation, to be removed in Python 3.10.

See https://docs.python.org/3/library/collections.html:
"Deprecated since version 3.3, will be removed in version 3.10: Moved
Collections Abstract Base Classes to the collections.abc module. For
backwards compatibility, they continue to be visible in this module
through Python 3.9."

lowRISC/ibex,lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,AmbiML/ibex