I made some small errors with the button tertiary colors that got caught in D10549 and [[ https://linear.app/comm/issue/ENG-6353/confirm-the-community-header-button-light-mode-colors#comment-60ae3477 | ENG-6353 ]], where I created two identical color variables for `--button-label-tertiary-default` + `--button-label-secondary-defaul` and I misspelled tertiary for `--button-background-tetirary-hover`. This diff addresses both of those mistakes