_brand.yml: google returning different font names confuses us

[cscheid]

This works:

typography: 
  fonts:
    - source: google
      family: 'Source Sans Pro'
  base: 
    family: 'Source Sans Pro'

This doesn't:

typography: 
  fonts:
    - source: google
      family: 'Source Sans 3'
  base: 
    family: 'Source Sans 3'

Even though "Source Sans 3" is the name of the font on Google Fonts. The issue appears to be that the CSS query returns Source Sans Pro as the name of the font, but we try to use Source Sans 3, and faceplant.

[gordonwoodhull]

Related to #11278 on the Typst side, which I stopgapped with some documentation because it seemed pretty rare.

But if the CSS query returns the actual font name, that's much better!