added workaround for git credentials

this is cherry-picked from osbmk. the cherry-pick was
performed by i, leah rowe. this is adapted from shmalebx's
patch there, in osboot

specifically, these patches from osbmk are being imported:

327a39ef058d5385bf8c1a1b09bac8db6a51b016

5139ad4be4df1835ce154f39161eef4f7c31ee1a

build

@@ -5,6 +5,7 @@
 #	Copyright (C) 2014, 2015, 2020, 2021 Leah Rowe <info@minifree.org>
 #	Copyright (C) 2015 Patrick "P. J." McDermott <pj@pehjota.net>
 #	Copyright (C) 2015, 2016 Klemens Nanni <contact@autoboot.org>
+#	Copyright (C) 2022, Caleb La Grange <thonkpeasant@protonmail.com>
 #
 #	This program is free software: you can redistribute it and/or modify
 #	it under the terms of the GNU General Public License as published by
@@ -19,6 +20,7 @@
 #	You should have received a copy of the GNU General Public License
 #	along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+./.gitcheck
 
 [ "x${DEBUG+set}" = 'xset' ] && set -v
 set -u -e
@@ -105,3 +107,5 @@ else
 	help
 	exit 0
 fi
+
+./.gitcheck clean