graphics/frogr: fix typo in Meson option name

meson.build:1:0: ERROR: Unknown options: "warnlevel"

https://gitlab.gnome.org/GNOME/frogr/-/commit/623d7e397baf

PR: 259080
Reported by: antoine (via exp-run)
Regressed by: https://github.com/mesonbuild/meson/commit/dbf2ace6ca1c

frogr