Fix a bug where lfs gc never worked. (#35198)

Fix #31113

After #22385 introduced LFS GC, it never worked due to a bug in the INI
library: fields in structs embedded more than one level deep are not
populated from the INI file.

This PR fixes the issue by replacing the multi-level embedded struct
with a single-level struct for parsing the cron.gc_lfs configuration.

Added a new test for retrieving cron settings to demonstrate the bug in
the INI package.

services/cron/tasks_extended_test.go

@@ -0,0 +1,51 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package cron
+
+import (
+	"testing"
+	"time"
+
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_GCLFSConfig(t *testing.T) {
+	cfg, err := setting.NewConfigProviderFromData(`
+[cron.gc_lfs]
+ENABLED = true
+RUN_AT_START = true
+SCHEDULE = "@every 2h"
+OLDER_THAN = "1h"
+LAST_UPDATED_MORE_THAN_AGO = "7h"
+NUMBER_TO_CHECK_PER_REPO = 10
+PROPORTION_TO_CHECK_PER_REPO = 0.1
+`)
+	assert.NoError(t, err)
+	defer test.MockVariableValue(&setting.CfgProvider, cfg)()
+
+	config := &GCLFSConfig{
+		BaseConfig: BaseConfig{
+			Enabled:    false,
+			RunAtStart: false,
+			Schedule:   "@every 24h",
+		},
+		OlderThan:                24 * time.Hour * 7,
+		LastUpdatedMoreThanAgo:   24 * time.Hour * 3,
+		NumberToCheckPerRepo:     100,
+		ProportionToCheckPerRepo: 0.6,
+	}
+
+	_, err = setting.GetCronSettings("gc_lfs", config)
+	assert.NoError(t, err)
+	assert.True(t, config.Enabled)
+	assert.True(t, config.RunAtStart)
+	assert.Equal(t, "@every 2h", config.Schedule)
+	assert.Equal(t, 1*time.Hour, config.OlderThan)
+	assert.Equal(t, 7*time.Hour, config.LastUpdatedMoreThanAgo)
+	assert.Equal(t, int64(10), config.NumberToCheckPerRepo)
+	assert.InDelta(t, 0.1, config.ProportionToCheckPerRepo, 0.001)
+}