tests: update sav/base_covar_int and sav/base_virtual_int because kernel has changed

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add base_covar_int2.nit and base_virtual_int2.nit

But new compilers are broken since they do the type-adaptation before the
covariance check.

Signed-off-by: Jean Privat <jean@pryen.org>