chore: update CODEOWNERS

[mikesposito]

Explanation

The CODEOWNERS file has been updated to match the new team handle.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
Administrative change to review ownership only; no product code or runtime behavior is affected.

Overview
Updates .github/CODEOWNERS so all files (*) are owned by @MetaMask/networks instead of @MetaMask/new-networks, ensuring review requests go to the renamed team.

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