bug#47092: Icecat sandbox causes issues with fonts in --pure env

[Martin via Bug reports for GNU Guix]

Problem fixed with the newest IceCat v91.2.0-guix0-preview1 in the
 guix c1ca853
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: c1ca85323d5246fc805a31e03b4164b8da08e930