docs: add noopener to verify social accounts example

[Madmin27]

Summary

• Adds noopener,noreferrer to the window.open(..., '_blank') example in the social verification guide.
• Fixes [docs] Add noopener/noreferrer to window.open example #1470.

Testing

• Ran node scripts/lint-mdx.js docs/base-account/guides/verify-social-accounts.mdx.
• The command currently fails because this file already has existing frontmatter and code block language issues unrelated to this one-line change.

[cb-heimdall]

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