download: compute version from Github tags for gvisor

Gvisor is the only one of our deployed components which use tags instead
of proper releases. So the tags scraping support will, for now, cater to
gvisor particularities, notably in the tag name format and the fact that
some older releases don't have the same URL scheme.

scripts/get_node_ids.sh

@@ -45,4 +45,7 @@ gh api graphql -H "X-Github-Next-Global-ID: 1" -f query='{
     crun: repository(owner: "containers", name: "crun") {
     id
     }
+    gvisor: repository(owner: "google", name: "gvisor") {
+    id
+    }
 }'