fix: use the right package manager in ci

[mahdiboomeri]

Currently, when using package managers other than npm, ci fails
example:

npm ERR! The `npm ci` command can only install with an existing package-lock.json or
npm ERR! npm-shrinkwrap.json with lockfileVersion >= 1. Run an install with npm@5 or
npm ERR! later to generate a package-lock.json file, then try again.

This PR uses https://github.com/antfu/ni to select the appropriate package manager.

[BracketJohn]

Great contribution, thanks @mahdiboomeri ❤️

Let's merge this wen CI goes through (:

[BracketJohn]

@mahdiboomeri can you checkout the CI failing? It's our smoke-detector check that tests whether the app starts + allows a status 200 curl (:

edit: seems to be a more general problem, I'm also looking into it in #21

[mahdiboomeri]

Hey @BracketJohn , Sorry i was away. Thanks for fixing the issue 💚