fix(assets-controllers): fix missing peer dependency

[ccharly]

Explanation

This peer dependency has been wrongly removed with my previous PR. I'm just re-adding it.

References

• refactor: use new @metamask/keyring-api layout (split packages) #4695

Changelog

N/A (will be unchanged for the next release)

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 highlighted breaking changes using the "BREAKING" category above as appropriate
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes