apt update fails since upgrading from Debian 11 to Debian 12.
Retypesetting from the screen of the machine with the failure (comments
and irrelevant parts were dropped):

# cat /etc/apt/sources.list
deb http://deb.debian.org/debian stable main
# apt update
Holen:1 http://deb.debian.org/debian stable InRelease [147 kB]
Fehl:1 http://deb.debian.org/debian stable InRelease
   Couldn't execute /usr/bin/apt-key to check
/var/lib/apt/lists/partial/deb.debian.org_debian_dists_stable_InRelease
…
# apt update -o Debug::Acquire::gpgv=1
Holen:1 http://deb.debian.org/debian stable InRelease [147 kB]
0% [Wird verarbeitet]inside VerifyGetsigners
Preparing to exec:  /usr/bin/apt-key --quiet --readonly verify
--status-fd 3 /tmp/apt.sig.TFfC34 /tmp/apt.data.IeOmfa
Read: [APTKEY:] ERROR Couldn't execute /usr/bin/apt-key to check
/var/lib/apt/lists/partial/deb.debian.org_debian_dists_stable_InRelease
…

However, the rest seems normal:

# ls -la /usr/bin/apt-key
-rwxr-xr-x 1 root root 27972 25. Mai 16:11 /usr/bin/apt-key
# head -1 /usr/bin/apt-key
#!/bin/sh
# ls -la /bin/sh
lrwxrwxrwx 1 root root 4  5. Jan 2023  /bin/sh -> dash
# which dash
/usr/bin/dash
# ls -la /usr/bin/dash
-rwxr-xr-x 1 root root 125640  5. Jan 2023  /usr/bin/dash
# /bin/sh
# exit
# apt-key
Usage: apt-key [--keyring file] [command] [arguments]
…
# ls -la
/var/lib/apt/lists/partial/deb.debian.org_debian_dists_stable_InRelease
-rw-r--r-- 1 root root 146972 10. Jun 12:05 
/var/lib/apt/lists/partial/deb.debian.org_debian_dists_stable_InRelease

Raised severity because this bug prevents me from properly upgrading the
system after the initial upgrade from Debian 11 to Debian 12.