third_party/sandboxroot: stabilize repo URLs

Metalink output is not stable, pin mirrors instead. We need to
set up our own caching proxy next, but this will do for now.

Change-Id: Ibc6ea9672890d88022a9310afb92db824226351d
Reviewed-on: https://review.monogon.dev/c/monogon/+/1087
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Tested-by: Jenkins CI
diff --git a/third_party/sandboxroot/regenerate.sh b/third_party/sandboxroot/regenerate.sh
index b9e4256..512d305 100755
--- a/third_party/sandboxroot/regenerate.sh
+++ b/third_party/sandboxroot/regenerate.sh
@@ -76,7 +76,7 @@
 
 EOF
 
-touch ${DIR}/repositories.bzl.in
+echo > ${DIR}/repositories.bzl.in
 
 # Create new sandbox root
 bazel ${BAZEL_ARGS} \