[guix] Fix source package

Summary: Since the archive is not created from the stdin files it needs the recursion.

Test Plan:

./contrib/guix/guix-clean && HOSTS="x86_64-linux-gnu" ./contrib/guix/guix-build

Check the source archive is not empty

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15650