[nextra] Fix some landing links

[gregnazario]

Description

This changes the careers link to the ecosystem job board, and fixes a link to the old aptos.dev site.

Checklist

• Do all Lints pass?
  • [] Have you ran pnpm spellcheck?
  • [] Have you ran pnpm fmt?
  • [] Have you ran pnpm lint?

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Name	Status	Preview	Comments	Updated (UTC)
developer-docs-nextra	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 17, 2024 5:45pm

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