msys2, pacmain -s 失敗: 簽章等級不明

Error:

來自 David Macek <david.macek.0@gmail.com> 的簽章信任等級不明

然後這一篇 有說明一個危險的方法，disable signature verification.

Disabling signature checking

Warning: Use with caution. Disabling package signing will allow pacman to install untrusted packages automatically.
If you are not concerned about package signing, you can disable PGP signature checking completely. 
Edit /etc/pacman.conf and uncomment the following line under [options]:

SigLevel = Never

You need to comment out any repository-specific SigLevel settings too because they override the global settings. 
This will result in no signature checking, which was the behavior before pacman 4. 
If you decide to do this, you do not need to set up a keyring with pacman-key. 
You can change this option later if you decide to enable package verification.