can't install "sudo apt-add-repository ppa:mosquitto-dev/mosquitto-ppa" per `make install-deps"

[squillace]

Description of the bug
on Ubuntu 20.04 WSL2, doing make install-deps to build (because installation fails due to #377 ) results in:

╭── ~/work/squillace/spiderlightning  main ✘✘✘ ✭
╰────▶ sudo apt-add-repository ppa:mosquitto-dev/mosquitto-ppa

More info: https://launchpad.net/~mosquitto-dev/+archive/ubuntu/mosquitto-ppa
Press [ENTER] to continue or Ctrl-c to cancel adding it.

Hit:1 https://packages.microsoft.com/repos/azure-cli focal InRelease
Hit:2 https://packages.microsoft.com/ubuntu/20.04/prod focal InRelease
Hit:3 http://archive.ubuntu.com/ubuntu focal InRelease
Hit:4 http://archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:5 https://download.docker.com/linux/ubuntu focal InRelease
Hit:6 http://archive.ubuntu.com/ubuntu focal-backports InRelease
Hit:7 http://security.ubuntu.com/ubuntu focal-security InRelease
Hit:8 https://download.mono-project.com/repo/ubuntu stable-focal InRelease
Hit:9 http://ppa.launchpad.net/mosquitto-dev/mosquitto-ppa/ubuntu focal InRelease
Get:10 https://packages.cloud.google.com/apt cloud-sdk InRelease [6361 B]
Err:10 https://packages.cloud.google.com/apt cloud-sdk InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B53DC80D13EDEF05
Hit:11 http://prerelease.keybase.io/deb stable InRelease
Reading package lists... Done
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://packages.cloud.google.com/apt cloud-sdk InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B53DC80D13EDEF05
W: Failed to fetch https://packages.cloud.google.com/apt/dists/cloud-sdk/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B53DC80D13EDEF05
W: Some index files failed to download. They have been ignored, or old ones used instead.

To Reproduce
sudo apt-add-repository ppa:mosquitto-dev/mosquitto-ppa on ubuntu 20.04 should do it

Additional context