Earlier quoted context omitted.
GPG signatures are kinda useless (when hosted on the same server). If I am able to replace the download I could probably deface also the pages where you give your signature and key fingerprint.
The point of GPG is to download the public key of the signer (in this case, the package maintainer). Then, you check it's bona fide, either by verifying that you have a trusted connection through your web of trust, or (more likely) by verifying the key id is mentioned in other trustworthy places (like legitimate Ansible and Bash scripts, etc.). After that, you have a trusted signature, and it doesn't matter if it the…
I believe you're confusing a PGP public key with a PGP signature for a particular file (made using said public key).