CI: Allow use of node16 for release jobs (rust-lang#3322)

actions/checkout@v3 is causing trouble in the `BuildBundle-Linux`
workflow as described in rust-lang#3321 .

This PR sets `ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true` to continue
using `node16` so we don't find issues with `node20` dependencies in
`ubuntu-18.04` jobs. This is the option recommended in this GitHub post:
https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

Resolves rust-lang#3321

.github/workflows/release.yml

@@ -16,6 +16,7 @@ on:
 
 env:
   RUST_BACKTRACE: 1
+  ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
 
 jobs:
   build_bundle_macos: