Fix Slack bot for npm publish failure

[lym953]

Motivation

NPM publish failed, but Slack bot step was skipped.

What does this PR do?

Fix the Slack bot triggered by npm publish failure, similar to https://github.com/DataDog/serverless-self-monitoring/pull/286

Testing Guidelines

Steps

1. Add this to publish.yml

   on:
   release:
   types: [created]
   + push:

2. Push

Result

Message was sent:

Additional Notes

Types of changes

• [x] Bug fix
• [ ] New feature
• [ ] Breaking change
• [ ] Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• [ ] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [ ] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog