npm deploy broken

## Describe the issue

in the deploy action the npm authentication seems to be broken:
https://github.com/matplotlib/ipympl/runs/5243522626?check_suite_focus=true
```
npm ERR! code ENEEDAUTH
npm ERR! need auth This command requires you to be logged in to https://registry.npmjs.org/
npm ERR! need auth You need to authorize this machine using `npm adduser`
```

This isn't important for `0.8.8` because we didn't bump the js version, but this will matter for the next one.

Start with the linked deploy action run and inspect where npm authentication fails. Compare the deployment configuration with the expected npm registry authentication, then verify that the action can authenticate successfully before the next JavaScript release.

Written by the indexing model from the issue text.