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/lib-git-p4.sh

@@ -175,7 +175,7 @@ stop_and_cleanup_p4d () {
 
 cleanup_git () {
 	retry_until_success rm -r "$git"
-	test_path_is_missing "$git" &&
+	test_must_fail test -d "$git" &&
 	retry_until_success mkdir "$git"
 }