APT repository not signed

Following the instructions for adding the key and APT repository, get the following on Ubuntu 20.04

```
sudo apt-get -y update
Ign:1 http://dl.bintray.com/v1/content/allegro/deb InRelease
Get:2 http://security.ubuntu.com/ubuntu focal-security InRelease [109 kB]
Get:3 http://dl.bintray.com/v1/content/allegro/deb Release [815 B]
Hit:4 http://archive.ubuntu.com/ubuntu focal InRelease
Ign:5 http://dl.bintray.com/v1/content/allegro/deb Release.gpg
Get:6 http://archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Get:7 http://archive.ubuntu.com/ubuntu focal-backports InRelease [101 kB]
Reading package lists... Done
E: The repository 'http://dl.bintray.com/v1/content/allegro/deb Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
```

Also noticed that releases post `1.4.2` are not on bintray. Is this intentional?