apt – How to fix “The repository ‘https://dl.bintray.com/loadimpact/deb stable InRelease’ is not signed.”?

On Ubuntu 20.04 I am trying to run the following command

sudo apt-get update

which fails with the following error:

E: Failed to fetch https://dl.bintray.com/loadimpact/deb/dists/stable/InRelease  403  Forbidden (IP: 443)
E: The repository 'https://dl.bintray.com/loadimpact/deb stable InRelease' 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.

I already tried to remove stuff like this

sudo rm -fr /var/lib/apt/lists/*

but this did not help. Anything else I can try to fix this problem?