test/mem_alloc_test.c: tfix in test_xaligned_alloc

test/mem_alloc_test.c: tfix in test_xaligned_alloc

Change "=" to "==" in "if ((exp == EXP_NONNULL) ...".

Fixes: d090695101a9 "test: add a sanity test for memory allocation functions"
Resolves: https://scan5.scan.coverity.com/#/project-view/65279/10222?selectedIssue=1662047
Resolves: https://scan5.scan.coverity.com/#/project-view/65279/10222?selectedIssue=1662049
Related: https://github.com/openssl/project/issues/1317
Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28238)