You need to install that key in a way that apt can use it.
The correct way is to put the key in /usr/share/keyrings, and then
reference it in the list file like this:
deb [signed-by=/usr/share/keyrings/kali-archive-keyring.gpg ...
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.
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