80-test_cmp_http.t: fix adaption of plan on 'certstatus' aspect of Mo…

…ck server

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from #18858)

test/recipes/80-test_cmp_http.t

@@ -171,7 +171,7 @@ sub test_cmp_http_aspect {
 
 indir data_dir() => sub {
     plan tests => 1 + @server_configurations * @all_aspects
-        + (grep(/^Mock$/, @server_configurations)
+        - (grep(/^Mock$/, @server_configurations)
            && grep(/^certstatus$/, @all_aspects));
 
     foreach my $server_name (@server_configurations) {