test(todoist): serve attachment from local test server

The test previously fetched the attachment from https://vikunja.io/testimage.jpg,
which caused flaky failures in CI when the external host was unreachable
(context deadline exceeded). Serve the local testimage.jpg via httptest and
temporarily allow non-routable IPs for the SSRF-safe client so the test is
hermetic and deterministic.

pkg/modules/migration/todoist/todoist_test.go

@@ -17,6 +17,8 @@
 package todoist
 
 import (
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"testing"
 	"time"
@@ -48,6 +50,20 @@ func TestConvertTodoistToVikunja(t *testing.T) {
 	exampleFile, err := os.ReadFile("../testimage.jpg")
 	require.NoError(t, err)
 
+	// Serve the attachment from a local test server so the test does not depend
+	// on an external host being reachable. The SSRF-safe client used by
+	// migration.DownloadFile rejects non-routable IPs by default, so allow them
+	// for the duration of this test.
+	prevAllowNonRoutable := config.OutgoingRequestsAllowNonRoutableIPs.GetBool()
+	config.OutgoingRequestsAllowNonRoutableIPs.Set("true")
+	t.Cleanup(func() {
+		config.OutgoingRequestsAllowNonRoutableIPs.Set(prevAllowNonRoutable)
+	})
+	attachmentServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		_, _ = w.Write(exampleFile)
+	}))
+	t.Cleanup(attachmentServer.Close)
+
 	makeTestItem := func(id, projectId string, hasDueDate, hasLabels, done bool) *item {
 		item := &item{
 			ID:            id,
@@ -245,7 +261,7 @@ func TestConvertTodoistToVikunja(t *testing.T) {
 					FileName:    "file.md",
 					FileType:    "text/plain",
 					FileSize:    12345,
-					FileURL:     "https://vikunja.io/testimage.jpg", // Using an image which we are hosting, so it'll still be up
+					FileURL:     attachmentServer.URL,
 					UploadState: "completed",
 				},
 				Posted: time1,