Disable issue subscribe button for guest users (#4095)

* disabled the button itself, but added the tooltip to the form, because it didn't work for the button and likely has something to do with JS
* added an integration test to verify the new logic

## Preview

|Signed in|Guest|
|-|-|
|![](/attachments/b1441565-6aec-4a72-a28f-6383914c8918)|![](/attachments/839cc58e-18cf-4a5d-a9d7-f0e3e2556c98)|

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/4095
Reviewed-by: Mai-Lapyst <mai-lapyst@noreply.codeberg.org>

tests/integration/issue_subscribe_test.go

@@ -0,0 +1,44 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"net/http"
+	"net/url"
+	"path"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIssueSubscribe(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, giteaURL *url.URL) {
+		session := emptyTestSession(t)
+		testIssueSubscribe(t, *session, true)
+	})
+}
+
+func testIssueSubscribe(t *testing.T, session TestSession, unavailable bool) {
+	t.Helper()
+
+	testIssue := "/user2/repo1/issues/1"
+	testPull := "/user2/repo1/pulls/2"
+	selector := ".issue-content-right .watching form"
+
+	resp := session.MakeRequest(t, NewRequest(t, "GET", path.Join(testIssue)), http.StatusOK)
+	area := NewHTMLParser(t, resp.Body).Find(selector)
+	tooltip, exists := area.Attr("data-tooltip-content")
+	assert.EqualValues(t, unavailable, exists)
+	if unavailable {
+		assert.EqualValues(t, "Sign in to subscribe to this issue.", tooltip)
+	}
+
+	resp = session.MakeRequest(t, NewRequest(t, "GET", path.Join(testPull)), http.StatusOK)
+	area = NewHTMLParser(t, resp.Body).Find(selector)
+	tooltip, exists = area.Attr("data-tooltip-content")
+	assert.EqualValues(t, unavailable, exists)
+	if unavailable {
+		assert.EqualValues(t, "Sign in to subscribe to this pull request.", tooltip)
+	}
+}