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

.gitcheck

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# SPDX-FileCopyrightText: 2022 Caleb La Grange <thonkpeasant@protonmail.com>
+# SPDX-License-Identifier: GPL-3.0-only
+
+Set_placeholder(){
+	git config user.name || git config user.name 'osbmkplaceholder'
+	git config user.email || git config user.email 'placeholder@osbmkplaceholder.com'
+}
+
+Clean(){
+	if [ "$(git config user.name)" = "osbmkplaceholder" ]; then
+		git config --unset user.name
+	fi
+
+	if [ "$(git config user.email)" = "placeholder@osbmkplaceholder.com" ]; then
+		git config --unset user.email
+	fi
+}
+
+Run(){
+if [ "${1}" = "clean" ]; then
+	Clean
+else
+	# Check if username and or email is set.
+	if ! git config user.name || git config user.email ; then
+		Set_placeholder
+	fi
+fi
+}
+
+Run >/dev/null