Fix a bug where lfs gc never worked. (#35198) (#35255)

Backport #35198 by @lunny

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.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/setting/cron_test.go

@@ -41,3 +41,56 @@ EXTEND = true
 	assert.Equal(t, "white rabbit", extended.Second)
 	assert.True(t, extended.Extend)
 }
+
+// Test_getCronSettings2 tests that getCronSettings can not handle two levels of embedding
+func Test_getCronSettings2(t *testing.T) {
+	type BaseStruct struct {
+		Enabled    bool
+		RunAtStart bool
+		Schedule   string
+	}
+
+	type Extended struct {
+		BaseStruct
+		Extend bool
+	}
+	type Extended2 struct {
+		Extended
+		Third string
+	}
+
+	iniStr := `
+[cron.test]
+ENABLED = TRUE
+RUN_AT_START = TRUE
+SCHEDULE = @every 1h
+EXTEND = true
+THIRD = white rabbit
+`
+	cfg, err := NewConfigProviderFromData(iniStr)
+	assert.NoError(t, err)
+
+	extended := &Extended2{
+		Extended: Extended{
+			BaseStruct: BaseStruct{
+				Enabled:    false,
+				RunAtStart: false,
+				Schedule:   "@every 72h",
+			},
+			Extend: false,
+		},
+		Third: "black rabbit",
+	}
+
+	_, err = getCronSettings(cfg, "test", extended)
+	assert.NoError(t, err)
+
+	// This confirms the first level of embedding works
+	assert.Equal(t, "white rabbit", extended.Third)
+	assert.True(t, extended.Extend)
+
+	// This confirms 2 levels of embedding doesn't work
+	assert.False(t, extended.Enabled)
+	assert.False(t, extended.RunAtStart)
+	assert.Equal(t, "@every 72h", extended.Schedule)
+}