Deprecation of Node 12 GitHub Actions

[pranasziaukas]

The Actions pipelines now issue a warning

Node.js 12 actions are deprecated. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/. Please update the following actions to use Node.js 16: zulip/github-actions-zulip/send-message@v1

which looks related to

github-actions-zulip/send-message/action.yml

Line 30 in 6ac0e0f

using: 'node12'

Maybe it's just a straightforward version bump?