seg: Add test "security" in meson.build

Oversight in 681d9e4 where the test has been added.

Reported-by: Justin Pryzby
Discussion: https://postgr.es/m/ZK5AgYxG4zLErD5O@telsasoft.com
Backpatch-through: 16

Author: michaelpq

contrib/seg/meson.build

@@ -53,6 +53,7 @@ tests += {
   'bd': meson.current_build_dir(),
   'regress': {
     'sql': [
+      'security',
       'seg',
     ],
   },