[depends] Fix qt download path

Summary:
The version we use is now obsolete and has been moved to the archive folder.
This will be reverted after we switch to Qt 6.

Test Plan: Run the guix builds

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18762