test_manifest_config_properties: use assertEqual

The method assertEquals is an deprecated alias for
assertEqual.
See: https://docs.python.org/3/library/unittest.html#deprecated-aliases

Change-Id: Id94ba6d6055bdc18b87c53e8729902bb278855aa
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/354035


Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Daniel Kutik <daniel.kutik@lavawerk.com>