Pin Undici to 6.13

[gonzaloriestra]

WHY are these changes introduced?

The @remix-run/node dependency requires undici ^6.10.1, which recently dropped support for Node <18.17 in v6.14.

But the CLI should work with Node > 18.12, so initializing a Remix app with that Node version is currently crashing:

Error coming from `npm install`

Command failed with exit code 1: npm install
npm ERR! code EBADENGINE
npm ERR! engine Unsupported engine
npm ERR! engine Not compatible with your version of node/npm: undici@6.14.1
npm ERR! notsup Not compatible with your version of node/npm: undici@6.14.1
npm ERR! notsup Required: {"node":">=18.17"}
npm ERR! notsup Actual:   {"npm":"8.19.2","node":"v18.12.0"}

WHAT is this pull request doing?

Adds a resolution/override to pin Undici to 6.13.0, which works with Node 18.12.

Test this PR

nvm use 18.12
shopify app init --template https://github.com/Shopify/shopify-app-template-remix#pin-undici 
shopify app init --template https://github.com/Shopify/shopify-app-template-remix#pin-undici --package-manager yarn
shopify app init --template https://github.com/Shopify/shopify-app-template-remix#pin-undici --package-manager pnpm
shopify app init --template https://github.com/Shopify/shopify-app-template-remix#pin-undici --package-manager bun

Checklist

Note: once this PR is merged, it becomes a new release for this template.

• I have added/updated tests for this change
• I have made changes to the README.md file and other related documentation, if applicable