multi: Modernize interface{} with any.

[jiangmencity]

This change replaces occurrences of interface{} with the predeclared identifier any, introduced in Go 1.18 as an alias for interface{}.

As noted in the Go 1.18 Release Notes:
This improves readability and aligns the codebase with modern Go conventions.

[davecgh]

Thanks for the PR. I don't see any reason not to even though it makes no real difference.

It'll be a little while before it is merged though as a couple of other ones will need to go in first to avoid rebase issues.

[jiangmencity]

Thanks for the PR. I don't see any reason not to even though it makes no real difference.

It'll be a little while before it is merged though as a couple of other ones will need to go in first to avoid rebase issues.

Thank you for your approval!