Save files in local storage as umask (#21198)

Go creates temporary files as 600, but sometimes we want the group to be able to read them (for example,
for another user to back up the storage)

This PR applies the umask to the renamed tmp files in local storage.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/util/file_unix_test.go

@@ -0,0 +1,36 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+//go:build !windows
+
+package util
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestApplyUmask(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "test-filemode-")
+	assert.NoError(t, err)
+
+	err = os.Chmod(f.Name(), 0o777)
+	assert.NoError(t, err)
+	st, err := os.Stat(f.Name())
+	assert.NoError(t, err)
+	assert.EqualValues(t, 0o777, st.Mode().Perm()&0o777)
+
+	oldDefaultUmask := defaultUmask
+	defaultUmask = 0o037
+	defer func() {
+		defaultUmask = oldDefaultUmask
+	}()
+	err = ApplyUmask(f.Name(), os.ModePerm)
+	assert.NoError(t, err)
+	st, err = os.Stat(f.Name())
+	assert.NoError(t, err)
+	assert.EqualValues(t, 0o740, st.Mode().Perm()&0o777)
+}