fix: accept preset as a table

[gmerzu]

The following config fails:

require("noice").setup({
  presets = {
    foo = {}
  }
})

with the error "expected table, got nil"

However, according to the doc (and the code) it should be acceptable to use a table in presents, the parameter presets is:
@class NoicePresets: table<string, NoicePreset|boolean>

This small PR fixes this issue.

[folke]

thanks!