Bump @solana/web3.js from 1.87.1 to 1.91.8 in /packages/demo

Bumps [@solana/web3.js](https://github.com/solana-labs/solana-web3.js) from 1.87.1 to 1.91.8.
- [Release notes](https://github.com/solana-labs/solana-web3.js/releases)
- [Commits](solana-foundation/solana-web3.js@v1.87.1...v1.91.8)

---
updated-dependencies:
- dependency-name: "@solana/web3.js"
  dependency-type: indirect
...

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