[MM-61466] Fix errcheck issues in server/channels/app/post_persistent_notification_test.go (#29207)

server/.golangci.yml

@@ -129,7 +129,6 @@ issues:
         channels/app/post.go|\
         channels/app/post_helpers_test.go|\
         channels/app/post_metadata.go|\
-        channels/app/post_persistent_notification_test.go|\
         channels/app/post_test.go|\
         channels/app/security_update_check.go|\
         channels/app/server.go|\

server/channels/app/post_persistent_notification_test.go

@@ -198,7 +198,8 @@ func TestSendPersistentNotifications(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()
 
-	th.App.AddUserToChannel(th.Context, th.BasicUser2, th.BasicChannel, false)
+	_, appErr := th.App.AddUserToChannel(th.Context, th.BasicUser2, th.BasicChannel, false)
+	require.Nil(t, appErr)
 
 	s := "Urgent"
 	tr := true
@@ -213,7 +214,7 @@ func TestSendPersistentNotifications(t *testing.T) {
 			},
 		},
 	}
-	_, appErr := th.App.CreatePost(th.Context, p1, th.BasicChannel, model.CreatePostFlags{})
+	_, appErr = th.App.CreatePost(th.Context, p1, th.BasicChannel, model.CreatePostFlags{})
 	require.Nil(t, appErr)
 
 	err := th.App.SendPersistentNotifications()