ci: Use Node 20 for CodeSandbox examples

[lachlancollins]

• Seems like CodeSandbox has added a Node 20 option (v20.12.2), but just hasn't documented it
• It's also enabled corepack by default, meaning we don't need a custom pnpm install script anymore
• The previous Node 18 version (v18.12.1) was incompatible with new versions of Next.js

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1 Ignored Deployment

Name	Status	Preview	Comments	Updated (UTC)
query	⬜️ Ignored (Inspect)	Visit Preview		Jun 29, 2024 6:14am

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[codesandbox-ci]

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Sandbox	Source
@tanstack/query-example-angular-basic	Configuration
@tanstack/query-example-react-basic-typescript	Configuration
@tanstack/query-example-solid-basic-typescript	Configuration
@tanstack/query-example-svelte-basic	Configuration
@tanstack/query-example-vue-basic	Configuration