Add missing scss/maps imports

[julien-deramond]

Maybe I'm wrong in my imports, but after the merge of 9f099d3, some bootstrap/scss/maps imports seem to be missing and to create errors:

Error: Undefined variable.
    ╷
358 │       values: $negative-spacers
    │               ^^^^^^^^^^^^^^^^^
    ╵
  bootstrap/scss/_utilities.scss 358:15  @import
  scss/custom.scss 36:9                  root stylesheet

or

Error: Undefined variable.
   ╷
20 │   @each $color, $value in $theme-colors-rgb {
   │                           ^^^^^^^^^^^^^^^^^
   ╵
  bootstrap/scss/_root.scss 20:27  @import
  scss/custom.scss 35:9            root stylesheet

[ffoodd]

I'm pretty sure it's tackled in another PR already but cannot retrieve it for now. 🤔

[ffoodd]

The fix is required and I'm unable to find another PR that would introduce the same fix.

@XhmikosR If you recall one, feel free to close this.

[XhmikosR]

It's probably a mistake. I can't find another PR so let's land this and we can revisit later.