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/t5580-clone-push-unc.sh

@@ -0,0 +1,77 @@
+#!/bin/sh
+
+test_description='various Windows-only path tests'
+. ./test-lib.sh
+
+if test_have_prereq CYGWIN
+then
+	alias winpwd='cygpath -aw .'
+elif test_have_prereq MINGW
+then
+	alias winpwd=pwd
+else
+	skip_all='skipping Windows-only path tests'
+	test_done
+fi
+
+UNCPATH="$(winpwd)"
+case "$UNCPATH" in
+[A-Z]:*)
+	# Use administrative share e.g. \\localhost\C$\git-sdk-64\usr\src\git
+	# (we use forward slashes here because MSYS2 and Git accept them, and
+	# they are easier on the eyes)
+	UNCPATH="//localhost/${UNCPATH%%:*}\$/${UNCPATH#?:}"
+	test -d "$UNCPATH" || {
+		skip_all='could not access administrative share; skipping'
+		test_done
+	}
+	;;
+*)
+	skip_all='skipping UNC path tests, cannot determine current path as UNC'
+	test_done
+	;;
+esac
+
+test_expect_success setup '
+	test_commit initial
+'
+
+test_expect_success clone '
+	git clone "file://$UNCPATH" clone
+'
+
+test_expect_success 'clone with backslashed path' '
+	BACKSLASHED="$(echo "$UNCPATH" | tr / \\\\)" &&
+	git clone "$BACKSLASHED" backslashed
+'
+
+test_expect_success push '
+	(
+		cd clone &&
+		git checkout -b to-push &&
+		test_commit to-push &&
+		git push origin HEAD
+	) &&
+	rev="$(git -C clone rev-parse --verify refs/heads/to-push)" &&
+	test "$rev" = "$(git rev-parse --verify refs/heads/to-push)"
+'
+
+test_expect_success MINGW 'remote nick cannot contain backslashes' '
+	BACKSLASHED="$(winpwd | tr / \\\\)" &&
+	git ls-remote "$BACKSLASHED" >out 2>err &&
+	test_i18ngrep ! "unable to access" err
+'
+
+test_expect_success 'unc alternates' '
+	tree="$(git rev-parse HEAD:)" &&
+	mkdir test-unc-alternate &&
+	(
+		cd test-unc-alternate &&
+		git init &&
+		test_must_fail git show $tree &&
+		echo "$UNCPATH/.git/objects" >.git/objects/info/alternates &&
+		git show $tree
+	)
+'
+
+test_done