lighten() is deprecated

The lighten function is deprecated and should be replaced with calling the adjust function (see docs below).

```
    ╷
240 │       background-color: lighten($grey-color-light, 6%);
    │                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
    ../../../../minima-2.5.2/_sass/minima/_base.scss 240:25
```

https://sass-lang.com/documentation/breaking-changes/color-functions/