Add pubdate for repository rss and add some tests (#33411)

Fix #33291

(cherry picked from commit dcd3014567f2b8be3fca01c20c2b3eabdc8f519e)

Conflicts:
	tests/integration/feed_user_test.go
  trivial context conflict

tests/integration/feed_repo_test.go

@@ -0,0 +1,36 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"encoding/xml"
+	"net/http"
+	"testing"
+
+	"code.gitea.io/gitea/tests"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFeedRepo(t *testing.T) {
+	t.Run("RSS", func(t *testing.T) {
+		defer tests.PrepareTestEnv(t)()
+
+		req := NewRequest(t, "GET", "/user2/repo1.rss")
+		resp := MakeRequest(t, req, http.StatusOK)
+
+		data := resp.Body.String()
+		assert.Contains(t, data, `<rss version="2.0"`)
+
+		var rss RSS
+		err := xml.Unmarshal(resp.Body.Bytes(), &rss)
+		require.NoError(t, err)
+		assert.Contains(t, rss.Channel.Link, "/user2/repo1")
+		assert.NotEmpty(t, rss.Channel.PubDate)
+		assert.Len(t, rss.Channel.Items, 1)
+		assert.EqualValues(t, "issue5", rss.Channel.Items[0].Description)
+		assert.NotEmpty(t, rss.Channel.Items[0].PubDate)
+	})
+}