[soil] Fetch tarball with https, not http

The new domain has required HTTPS, which seems a bit annoying, but it is
probably right.

soil/common.sh

@@ -88,7 +88,7 @@ git-commit-url() {
   commit_hash=$(cat _tmp/soil/commit-hash.txt)
 
   # https:// not working on Github Actions?
-  local url="http://$SOIL_HOST/${prefix}jobs/git-$commit_hash"
+  local url="https://$SOIL_HOST/${prefix}jobs/git-$commit_hash"
 
   echo $url
 }