wc_ValidateEccsiPair() reports an off-curve PVT via wc_ecc_is_point(), whose
error code is backend-dependent: the mp-based check (classic / SP_MATH_ALL /
fast-math) returns IS_POINT_E, but the minimal WOLFSSL_SP_MATH backend routes
through sp_ecc_is_point_*(), which returns MP_VAL for a point not on the curve
(and eccsi.c only remaps -1 -> IS_POINT_E, not MP_VAL). Select the expected
code per backend so the all-pq-sp-math CI config (--enable-sp-math) passes.
Verified: full unit.test --api under --enable-all --enable-sp-math --enable-sp-asm
reports 0 failures.