fix: update sepolia USDC bridge addresses in the bridge ui in README

[paulallensuxs]

Changed linea USDC bridge contract addresses in README to the working addresses as in bridge-ui/.env.production

Checklist

• I wrote new tests for my new core changes.
• I have successfully ran tests, style checker and build against my new changes locally.
• I have informed the team of any breaking changes if there are any.

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