nixos/postgresql: MemoryDenyWriteExecute must be off when doing JIT

The test breaks like this otherwise:

    machine # WARNING:  error during JITing: Permission denied
    machine # [   14.012280] postgres[913]: [913] WARNING:  error during JITing: Permission denied
    machine # ERROR:  failed to look up symbol "evalexpr_0_1": Failed to materialize symbols: { (main, { evalexpr_0_1, evalexpr_0_0 }) }

nixos/modules/services/databases/postgresql.nix

@@ -630,7 +630,7 @@ in
             PrivateTmp = true;
             ProtectHome = true;
             ProtectSystem = "strict";
-            MemoryDenyWriteExecute = true;
+            MemoryDenyWriteExecute = lib.mkDefault (config.services.postgresql.settings.jit == "off");
             NoNewPrivileges = true;
             LockPersonality = true;
             PrivateDevices = true;