Fix warnings in ee/spec/frontend/design_management/router_spec.js

The following discussion from !10222 (merged) should be addressed:

• @winh started a discussion: (+2 comments)

  There are new warnings in the Jest suite:

      console.warn node_modules/@gitlab/ui/dist/index.js:626
        Icon sizes 1 - 5 are deprecated, please use 'sm', 'md' and 'lg' instead.
      console.warn node_modules/@gitlab/ui/dist/index.js:626
        Icon sizes 1 - 5 are deprecated, please use 'sm', 'md' and 'lg' instead.

  They are not failing the test though and we need to change that.