Refactor template & test related code (#32938)

Move some legacy code from "base" package to proper packages.

modules/test/utils_test.go

@@ -0,0 +1,17 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSetupGiteaRoot(t *testing.T) {
+	t.Setenv("GITEA_ROOT", "test")
+	assert.Equal(t, "test", SetupGiteaRoot())
+	t.Setenv("GITEA_ROOT", "")
+	assert.NotEqual(t, "test", SetupGiteaRoot())
+}