CI: do not pass --llvm to grcov, since we have a gcc+llvm build
CI: do not pass --llvm to grcov, since we have a gcc+llvm build

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/709>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg