Race condition while starting sandboxed system services

**Image I'm using:**

Bottlerocket 1.54.0 and onwards

**What I expected to happen:**

System initializes

**What actually happened:**

The system failed to boot due to a race condition between sandboxed system services and the `/tmp` mount. systemd will attempt to create directories under `/tmp` before the mount exists, resulting in errors like this:

```
[FAILED] Failed to start D-Bus System Message Bus.
See 'systemctl status whippet.service' for details.
```

**How to reproduce the problem:**

The best way to reproduce is to use a custom AMI (which won't be cached by EBS, hitting the race condition faster) in a smaller region. I launched 10 instances and 6 failed to start with that same error.