merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/t2014-checkout-switch.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+test_description='Peter MacMillan'
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo Hello >file &&
+	git add file &&
+	test_tick &&
+	git commit -m V1 &&
+	echo Hello world >file &&
+	git add file &&
+	git checkout -b other
+'
+
+test_expect_success 'check all changes are staged' '
+	git diff --exit-code
+'
+
+test_expect_success 'second commit' '
+	git commit -m V2
+'
+
+test_expect_success 'check' '
+	git diff --cached --exit-code
+'
+
+test_done