When you say 'the right to serve the font from your webserver' -- in this case, 'your webserver' may simply be GitHub's web-server, a service they provide to you as part of your payment to them (either because it's part of the app you host on GH, or as a piece of the website hosted via GH Pages [0])...
Assuming that the font's usage for the repo'd app/site is OK per the license terms, then I'd be surprised if its availability in the repo would solely cause it to fall out of compliance with the license. I suppose that the licensor could, if they chose to do so, specifically include terms to preclude the usage of the font on any sites hosted with "repository or other open file listing indexes", or any other similarly restrictive arbitrary terms.