Revert "guix: bump time-machine to 7bf1d7aeaffba15c4f680f93ae88fbef25…

…427252"

This reverts commit 5d9f12a.

Windows defender hits us with a Trojan:Win32/ClipBanker.GA!MTB

contrib/guix/libexec/prelude.bash

@@ -51,7 +51,7 @@ fi
 time-machine() {
     # shellcheck disable=SC2086
     guix time-machine --url=https://github.com/tobtoht/guix.git \
-                      --commit=7bf1d7aeaffba15c4f680f93ae88fbef25427252 \
+                      --commit=f0bb724211872cd6158fce6162e0b8c73efed126 \
                       --cores="$JOBS" \
                       --keep-failed \
                       --fallback \