Fix submodule parsing (#32571)

Fix #32568, parse `.gitmodules` correctly

---------

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

modules/git/config_submodule_test.go

@@ -0,0 +1,49 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestConfigSubmodule(t *testing.T) {
+	input := `
+[core]
+path = test
+
+[submodule "submodule1"]
+	path = path1
+	url =	https://gitea.io/foo/foo
+	#branch = b1
+
+[other1]
+branch = master
+
+[submodule "submodule2"]
+	path = path2
+	url =	https://gitea.io/bar/bar
+	branch = b2
+
+[other2]
+branch = main
+
+[submodule "submodule3"]
+	path = path3
+	url =	https://gitea.io/xxx/xxx
+`
+
+	subModules, err := configParseSubModules(strings.NewReader(input))
+	assert.NoError(t, err)
+	assert.Len(t, subModules.cache, 3)
+
+	sm1, _ := subModules.Get("path1")
+	assert.Equal(t, &SubModule{Path: "path1", URL: "https://gitea.io/foo/foo", Branch: ""}, sm1)
+	sm2, _ := subModules.Get("path2")
+	assert.Equal(t, &SubModule{Path: "path2", URL: "https://gitea.io/bar/bar", Branch: "b2"}, sm2)
+	sm3, _ := subModules.Get("path3")
+	assert.Equal(t, &SubModule{Path: "path3", URL: "https://gitea.io/xxx/xxx", Branch: ""}, sm3)
+}