CI: fix broken FreeBSD CI by setting -Dlibsfdo:b_ndebug=false

CI: fix broken FreeBSD CI by setting -Dlibsfdo:b_ndebug=false

...because with with

    meson setup build -Dbuildtype=release -Db_ndebug=true \
        --werror --force-fallback-for=libsfdo

we get the following warning:

    In file included from ../subprojects/libsfdo/common/dirs.c:5:
    ../subprojects/libsfdo/include/common/membuild.h: In function ‘sfdo_membuild_validate’:
    ../subprojects/libsfdo/include/common/membuild.h:29:65: error: unused parameter ‘membuild’ [-Werror=unused-parameter]
       29 | static inline void sfdo_membuild_validate(struct sfdo_membuild *membuild) {

...because `sfdo_membuild_validate()` contains nothing but an `assert()`
and that therefore results in an `unused-parameter` warning with `NDEBUG`.

https://gitlab.freedesktop.org/vyivel/libsfdo/-/blob/main/include/common/membuild.h?ref_type=heads#L30