Add node-fetch

[danmichaelo]

Fixes #305

Installed node-fetch 2.6.7, which is the same version used by @octokit/request:

npm ls node-fetch
github-script@6.3.3
├─┬ @octokit/core@3.6.0
│ └─┬ @octokit/request@5.6.3
│   └── node-fetch@2.6.7 deduped
└── node-fetch@2.6.7

The bundle size only increased from 772,787 to 772,991 bytes, so seems like re-use works well.

If we installed node-fetch 3 instead, the bundle size would increase to 1,045,047 bytes. Most likely the difference would hardly be noticeable, but on the other hand there aren't that many important improvements in node-fetch 3 as far as I'm aware, so perhaps it's still better to use node-fetch 2 to save 270 kB?

Of course, once Node18 is available from GitHub, node-fetch is no longer needed, but seems like that may take some time.

(Updated ncc because I had a build problem with node-fetch 3)

[joshmgross]

Looks like the check-dist check is failing. Could you try re-running npm run build?

[joshmgross]

Looks like the check-dist check is failing

Actually that's failing on main too, I'll investigate 🤔
https://github.com/actions/github-script/actions/runs/4011143550

[joshmgross]

Thanks for your contribution! I'll go ahead and release a new version with this

[joshmgross]

This is now available in https://github.com/actions/github-script/releases/tag/v6.4.0

I'll update v6 tomorrow once I've validated that there are no unexpected issues.