Bug#1129662: release-notes: upgrading.html#adding-apt-internet-sources uses .pgp files but they are .gpg files on debian 12

Package: release-notes
Severity: normal
X-Debbugs-Cc: [email protected]

Dear Maintainer,

I use this doc since a few months to upgrade Debian 12 hosts.
I believe the section #adding-apt-internet-sources has changed recently (<1month?)
It now presents this line:
```
Signed-By: /usr/share/keyrings/debian-archive-keyring.pgp
```
And I belive the correct line for Debian 12 is:
```
Signed-By: /usr/share/keyrings/debian-archive-keyring.pgp
```
As the .pgp file can't be found. But the .gpg version is here.
So I have this error when adding the new source:
```
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://security.debian.org/debian-security trixie-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BDE6D2B9216EC7A8 NO_PUBKEY 8E9F831205B4BA95
W: Failed to fetch https://security.debian.org/debian-security/dists/trixie-security/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BDE6D2B9216EC7A8 NO_PUBKEY 8E9F831205B4BA95
W: Some index files failed to download. They have been ignored, or old ones used instead.
```
Setting the Signed-By option with the .gpg filename fixes it, and I can
update and upgrade as wanted

Thanks for reading!