nixos/redmine: Enable MountAPIVFS hardening in service config

This setting is already implied by others, but add it for completeness
as well. For documentation see
https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html#MountAPIVFS=

Signed-off-by: Felix Singer <felixsinger@posteo.net>

nixos/modules/services/misc/redmine.nix

@@ -461,6 +461,7 @@ in
         CapabilityBoundingSet = "";
         LockPersonality = true;
         MemoryDenyWriteExecute = true;
+        MountAPIVFS = true;
         NoNewPrivileges = true;
         PrivateDevices = true;
         PrivateMounts = true;