wireit ignores npm's shell-script setting

[tao-cumplido]

In #648 @aomarks already mentions that the shell-script setting isn't supported yet, but there was no explicit issue for it yet.

I use shell-script=/bin/zsh for some projects because ** globs work as expected instead of the default shell (at least on macOS).

For example when I run the following command with npm's default shell sh it only matches a subset of the expected match

> node -e "console.log(process.argv)" src/**/*.test.ts
[ '/path/to/my/project', 'src/test/a.test.ts', 'src/test/b.test.ts' ]
> 

but there's also a src/test/sub/a.test.ts which is not included in sh's expansion.

The actual command I noticed this with is tsx --test src/**/*.test.ts which uses tsx to run my tests written in TS with node's builtin test runner.

[tao-cumplido]

Found a workaround: running the command through npx automatically picks up the npm settings.

npx -c 'tsx --test src/**/*.test.ts'