Fix bug with setting theme in compatability mode resulting in a noop

This issue was originally reported by @janhassel where the compat theme was not able to have its value changed.

Code to reproduce:

@use '@carbon/react/scss/reset';
@use '@carbon/react/scss/compat/themes';
@use '@carbon/react/scss/compat/theme' with (
  $theme: themes.$g90
);

body {
  background: theme.$background;
  color: theme.$text-primary;
}

Here, we expected the tokens to use values from the g90 theme but they use the value from the white theme instead. It seems like this is related to the issue Jan reported in that the theme would not allow you to correctly retrieve interactive-01 as a token because the themes were not being merged

[joshblack]

@janhassel I think until we update the code to use the new tokens we’ll run into this issue since the theme is looking for tokens that don’t exist. I’ll make sure we will go and update them in the next release though so that you can configure the theme as expected 👍

[joshblack]

@janhassel thanks!

Side-note: I think you’ll have to always use the second form just as a heads up otherwise you’ll get the error where a module has been used before it’s being configured.