I tried the entire, 4.1 section of troubleshooting invalid signature errors and I keep getting the same error. I could just disable signature checking but I think that choice will bite back eventually.
Seperately
I tried
sudo pacman-key --refresh Sven
and got
gpg: error retrieving 'sh@lutzhaase.com' via WKD: No data
gpg: error reading key: No data
gpg: key 39E4B877E62EB915: "Sven-Hendrik Haase <sh@lutzhaase.com>" not changed
gpg: Total number processed: 1
gpg: unchanged: 1
pub rsa4096 2011-09-10 [SC]
8FC15A064950A99DD1BD14DD39E4B877E62EB915
uid [marginal] Sven-Hendrik Haase <sh@lutzhaase.com>
uid [ full ] Sven-Hendrik Haase <svenstaro@archlinux.org>
uid [marginal] Sven-Hendrik Haase <svenstaro@gmail.com>
sub rsa4096 2022-07-10 [A]
sub rsa4096 2011-09-10 [E]