To quote myself:
This should work for you.
Edit:
You can also check whether the file /etc/apt/trusted.gpg.d/graphics_darktable.gpg exists:
$ ls -al /etc/apt/trusted.gpg.d/graphics_darktable.gpg
-rw-r--r-- 1 root root 1110 May 29 13:24 /etc/apt/trusted.gpg.d/graphics_darktable.gpg
And print some information about the key (e.g. the expiry date) with the gpg command:
$ gpg --show-keys /etc/apt/trusted.gpg.d/graphics_darktable.gpg
pub rsa2048 2017-12-26 [SC] [expires: 2024-07-26]
3247B7519EDBEAB422E900A3040524A84C70D8B5
uid graphics:darktable OBS Project <graphics:darktable@build.opensuse.org>
Notice that the key that I have installed has an expiry date of July 26, 2024.
The previous key from 2020 looked like this and expired back in May:
$ gpg --show-key graphics_darktable_2020.gpg
pub rsa2048 2017-12-26 [SC] [expired: 2022-05-16]
3247B7519EDBEAB422E900A3040524A84C70D8B5
uid graphics:darktable OBS Project <graphics:darktable@build.opensuse.org>
You notice that the key ID is actually the same, but it has been re-published with a new expiry date.