tools: buildman: fix non-existing SafeConfigParser in Python 3.12+

SafeConfigParser was renamed back in Python 3.2 (yes, no typo) to
ConfigParser[1], but it was still working as an alias until it got
removed in 3.12[2].

[1] https://docs.python.org/3.8/whatsnew/3.2.html#configparser
[2] https://github.com/python/cpython/pull/92503



Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>