Description:
The setup-node action is a popular tool for setting up Node.js environments in GitHub Actions workflows. Currently, it supports npm, pnpm, and yarn as package managers. However, there’s a need to include support for Bun, a faster JavaScript runner.

Justification:
Bun offers performance improvements over traditional JavaScript runners, making it an attractive choice for developers. By adding support for Bun in the setup-node action, GitHub Actions workflows can benefit from its speed and efficiency.

Are you willing to submit a PR?
I will have a look.