guix: Rename MacOS binaries to unsigned.tar.gz

The MacOS binaries are unsigned and therefore also unusable on MacOS.
Indicate as such by naming the tarball "unsigned".

contrib/guix/libexec/build.sh

@@ -362,8 +362,8 @@ mkdir -p "$DISTSRC"
                 find "${DISTNAME}" -print0 \
                     | sort --zero-terminated \
                     | tar --create --no-recursion --mode='u+rw,go+r-w,a+X' --null --files-from=- \
-                    | gzip -9n > "${OUTDIR}/${DISTNAME}-${HOST}.tar.gz" \
-                    || ( rm -f "${OUTDIR}/${DISTNAME}-${HOST}.tar.gz" && exit 1 )
+                    | gzip -9n > "${OUTDIR}/${DISTNAME}-${HOST}-unsigned.tar.gz" \
+                    || ( rm -f "${OUTDIR}/${DISTNAME}-${HOST}-unsigned.tar.gz" && exit 1 )
                 ;;
         esac
     )  # $DISTSRC/installed