chore(brand): deduplicate font imports

[gadenbuie]

Small change to deduplicate font imports. Prior to this change, a brand like

typography:
  fonts:
    - family: IBM Plex Mono
      source: google

  monospace:
    family: IBM Plex Mono
  monospace-inline:
    family: IBM Plex Mono
  monospace-block:
    family: IBM Plex Mono

Would result in three @import statements for "IBM Plex Mono"

@import"https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:ital,wght@0,400;0,700;1,400;1,700&display=swap";
@import"https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:ital,wght@0,400;0,700;1,400;1,700&display=swap";
@import"https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:ital,wght@0,400;0,700;1,400;1,700&display=swap";

After this PR, identical imports are dropped:

@import"https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:ital,wght@0,400;0,700;1,400;1,700&display=swap";

[cscheid]

Looks great, thanks.