GDPR Inform Block introduces brand colors into socialbase

Problem

Socialbase should provide structure only and should not provide coloring for blocks as that could break the color schemes of extending themes such as socialblue.

The GDPR Inform Block provides a (non variable) color to the card title of the GDPR inform and consent block.

Proposed Solution

Move the color to the socialblue theme and utilise the $brand-primary color variable.

An alternative would be to add the `.bg-primary` class. We can't add this in the block build array itself because it's in an external module. This could be done in a preprocess hook but it's semantically more correct to do this by targetting the .card__title class in case someone else wants to make it the brand-secondary color or highlight it in some other way.