Add rel="nofollow" to issue filter links

The issue filter links should not be crawled by search engines, because
they they only filter results, and contain nothing new, yet, they put a
considerable load on the server.

To stop - well behaving - search engines from following these links, add
a `rel="nofollow"` property to them. The same property is already
present on the archive download links, and plenty of other places.

Fixes #2361.

Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>

tests/integration/issue_test.go

@@ -1,4 +1,5 @@
 // Copyright 2017 The Gitea Authors. All rights reserved.
+// Copyright 2024 The Forgejo Authors c/o Codeberg e.V.. All rights reserved.
 // SPDX-License-Identifier: MIT
 
 package integration
@@ -797,3 +798,20 @@ func TestCommitRefComment(t *testing.T) {
 		assert.Contains(t, event, "referenced this issue")
 	})
 }
+
+func TestIssueFilterNoFollow(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	req := NewRequest(t, "GET", "/user2/repo1/issues")
+	resp := MakeRequest(t, req, http.StatusOK)
+	htmlDoc := NewHTMLParser(t, resp.Body)
+
+	// Check that every link in the filter list has rel="nofollow".
+	filterLinks := htmlDoc.Find(".issue-list-toolbar-right a[href*=\"/issues?q=\"]")
+	assert.True(t, filterLinks.Length() > 0)
+	filterLinks.Each(func(i int, link *goquery.Selection) {
+		rel, has := link.Attr("rel")
+		assert.True(t, has)
+		assert.Equal(t, "nofollow", rel)
+	})
+}