chore: change deprecated sass functions and warnings

[airween]

This PR changes two errors in newest hugo versions:

ERROR deprecated: resources.ToCSS was deprecated in Hugo v0.128.0 and subsequently removed. Use css.Sass instead.
ERROR deprecated: resources.PostCSS was deprecated in Hugo v0.128.0 and subsequently removed. Use css.PostCSS instead.

and fixes many warnings like

WARN  Dart Sass: DEPRECATED [mixed-decls]: file:///PATH/TO/SOURCEROOT/themes/dot-org-hugo-theme/assets/scss/_typography.scss:7:4: Sass's behavior for declarations that appear after nested
rules will be changing to match the behavior specified by CSS in an upcoming
version. To keep the existing behavior, move the declaration above the nested
rule. To opt into the new behavior, wrap the declaration in `& {}`.