security: analyze dependencies for malicious behavior

[varunsh-coder]

This PR

1. Adds harden-runner GitHub Action to the workflow.
2. Sets the token permission for the workflow to contents: read. This is a security best practice and gets you are higher Scorecard score. Your package currently has score of 5.7 out of 10
3. Updates the branch in the workflow to main. It was set to master earlier, so the workflow was not running.

harden-runner GitHub Action detects hijacked dependencies and compromised build tools. It correlates outbound traffic with each step of the workflow so you can see what processes are calling what endpoints. This is the analysis when run on a fork: https://app.stepsecurity.io/github/varunsh-coder/regenerator/actions/runs/1928466475

You can restrict traffic to the allowed endpoints for future runs which will block calls that compromised dependencies typically make, and an annotation will be shown in such cases. You do not need to grant any permission or install any App to use this, and the action (and agent the action uses) are open source.

Information on how harden-runner could have detected past package hijacks can be found here: https://github.com/step-security/supply-chain-goat. Do share feedback to improve the harden-runner GitHub Action developer experience. Thanks!

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