setup-alpine/index.js

const { exec } = require('node:child_process');
var additional = process.env.INPUT_ADDITIONAL;
exec('apk add bash git ' + additional, (err, output) => {
    if (err) {
        console.log("Something went wrong...");
        console.log(output);
    } else {
        console.log("Successfully installed packages!");
    }
})