test/recipes/30-test_afalg.t: set OPENSSL_ENGINES correctly

The afalg engine was moved down from engines/afalg/ to engines/, but
the test wasn't changed accordingly.  This was undetected because the
test program didn't fail when it couldn't load the engine.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5270)