Minor Changes to Decrypt API Key within LA Guide

[spacesailor24]

• I've updated the required NodeJS version to v20 from v19 When attempting to run yarn with v19, I get the following error:

  yarn install v1.22.22
  warning ../../../package.json: No license field
  [1/4] 🔍  Resolving packages...
  [2/4] 🚚  Fetching packages...
  error node-addon-api@7.1.0: The engine "node" is incompatible with this module. Expected version "^16 || ^18 || >= 20". Got "19.9.0"
  error Found incompatible module.
  info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.

  Upgrading to v20 fixes the error

• I updated the package.json start script command because the existing command was giving me the error:

  yarn run v1.22.22
  warning ../../../package.json: No license field
  $ ts-node-esm src/index.ts
  TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts" for /Users/whyit/tmp/developer-guides-code/decrypt-api-key-in-action/src/index.ts
    at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:160:9)
    at defaultGetFormat (node:internal/modules/esm/get_format:203:36)
    at defaultLoad (node:internal/modules/esm/load:143:22)
    at async nextLoad (node:internal/modules/esm/hooks:865:22)
    at async nextLoad (node:internal/modules/esm/hooks:865:22)
    at async Hooks.load (node:internal/modules/esm/hooks:448:20)
    at async MessagePort.handleMessage (node:internal/modules/esm/worker:196:18) {
  code: 'ERR_UNKNOWN_FILE_EXTENSION'
  }
  error Command failed with exit code 1.
  info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.