chore: add Yarn v1 allow-scripts in update script

[MikeMcC399]

Situation

With the rollout of npm@11.16.0 to Node.js 24.18.0 Active LTS, running the script scripts/update-cypress-latest-yarn.sh results in a warning:

npm warn allow-scripts 1 package has install scripts not yet covered by allowScripts:
npm warn allow-scripts   yarn@1.22.22 (preinstall: :; (node ./preinstall.js > /dev/null 2>&1 || true))

Change

Modify scripts/update-cypress-latest-yarn.sh to install Yarn Classic with:

npm install yarn@1 --global --allow-scripts=yarn

Verification

Ubuntu 24.04.4 LTS, Node.js 24.18.0 LTS and execute:

./scripts/update-cypress-latest-yarn.sh

Confirm no npm allow-scripts warnings appear.

---

Note

Low Risk
Dev-only script change with no runtime, auth, or production impact.

Overview
Updates both global Yarn Classic installs in scripts/update-cypress-latest-yarn.sh from npm install yarn@1 -g to npm install yarn@1 --global --allow-scripts=yarn.

This opts in to Yarn v1’s install lifecycle scripts under npm 11.16+ (e.g. on Node.js 24.18 LTS), so running the Cypress example update script no longer emits allow-scripts warnings for yarn@1.22.22.

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[cypress-app-bot]

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