scripts: west: commands: tests: dfu_util: fix test under Python 3.12

Use "call_args_list" from unittest.mock instead of "called_with" for
verifying the arguments supplied to the dfu-util west runner.

This aligns the assert with the rest of the test case and fixes the
dfu-util west runner test when running under Python 3.12.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>