Use keyring for apt::source

[PeterAlfonsLoch]

Pull Request (PR) description

Adding the path to keyring to the apt::source fixes warnings happening on apt update

This Pull Request (PR) fixes the following issues

apt-key is deprecated and the nginx keys are stored in legacy trusted.gpg. This returns warnings:

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://nginx.org/packages/debian bookworm InRelease: The following signatures were invalid: EXPKEYSIG ABF5BD827BD9BF62 nginx signing key <signing-key@nginx.com>
W: Failed to fetch https://nginx.org/packages/debian/dists/bookworm/InRelease  The following signatures were invalid: EXPKEYSIG ABF5BD827BD9BF62 nginx signing key <signing-key@nginx.com>
W: Some index files failed to download. They have been ignored, or old ones used instead.```

[kenyon]

#1610 is solving this in a different way, so I'll close this.