List RFN into Fontbakery

Add "Zalando Sans" to Fontbakery's exception list—only after the legal team sent the email to GF;
https://github.com/fonttools/fontbakery/blob/main/Lib/fontbakery/data/googlefonts/reserved_font_name_exceptions.txt

cf https://googlefonts.github.io/gf-guide/license-file.html