fix: ignore expired artifacts for quota calculation (#7976)

- Expired artifacts are kept in the database but the artifact has been deleted from the storage. Ignore them for the quota calculation.
- Added unit test.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7976
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Reviewed-by: Otto <otto@codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

models/quota/used_test.go

@@ -0,0 +1,23 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package quota
+
+import (
+	"testing"
+
+	"forgejo.org/models/unittest"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetUsedForUser(t *testing.T) {
+	defer unittest.OverrideFixtures("models/fixtures/TestGetUsedForUser/")()
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	used, err := GetUsedForUser(t.Context(), 5)
+	require.NoError(t, err)
+
+	assert.EqualValues(t, 4096, used.Size.Assets.Artifacts)
+}