revert(3p/git): Revert merge of git upstream at v2.26.2

This causes cgit to serve error pages, which is undesirable.

This reverts commit 5229c9b232, reversing
changes made to f2b211131f.

third_party/git/t/t7505-prepare-commit-msg-hook.sh

@@ -241,7 +241,13 @@ test_rebase () {
 			git add b &&
 			git rebase --continue
 		) &&
-		git log --pretty=%s -g -n18 HEAD@{1} >actual &&
+		if test "$mode" = -p # reword amended after pick
+		then
+			n=18
+		else
+			n=17
+		fi &&
+		git log --pretty=%s -g -n$n HEAD@{1} >actual &&
 		test_cmp "$TEST_DIRECTORY/t7505/expected-rebase${mode:--i}" actual
 	'
 }