guix: update time-machine to 160f78a4d92205df986ed9efcce7d3aac188cb24

In our time-machine environment this changes the following:

GCC 10.3.0 -> 10.4.0
Binutils 2.37 -> 2.38
Linux Libre Headers 5.15.37 -> 5.15.127
git 2.36.0 -> 2.41.0
mingw-w64 8.0.0 -> 11.0.1
NSIS 3.05 -> 3.09
xorriso 1.5.2 -> 1.5.6.pl02
Python 3.9 -> 3.10.7
Python-asn1crypto 1.4.0 -> 1.5.1

GCC 12.3.0 becomes available.
LLVM 15.0.7 becomes available.

contrib/guix/libexec/prelude.bash

@@ -51,7 +51,7 @@ fi
 time-machine() {
     # shellcheck disable=SC2086
     guix time-machine --url=https://git.savannah.gnu.org/git/guix.git \
-                      --commit=998eda3067c7d21e0d9bb3310d2f5a14b8f1c681 \
+                      --commit=160f78a4d92205df986ed9efcce7d3aac188cb24 \
                       --cores="$JOBS" \
                       --keep-failed \
                       --fallback \