Not showing warning when using a taken GPU

### Nomad version
nomad server: `Nomad v1.6.1` + patch with #18141
nomad client: `Nomad v1.6.1` + patch with #18141

### Operating system and Environment details
Plugin "nomad-driver-podman" v0.5.1
Plugin "nomad-device-nvidia" v1.0.0

### Issue
I created a patch with the solution provides in #18141 to test on our cluster. While testing I discovered that if a GPU or multiple GPU are already used in jobs, nomad will not give a warning about this and will place the job without using those GPUs.

### Reproduction steps
1. Create a job file where you use multiple GPUs and set constraint based on their UUID.
2. Create a new job file where you use one or more GPUs that is already used in the first job.

#### Expected Result
Throw an warning like `WARNING: Failed to place all allocations.`

#### Actual Result
Place the job on the client.

### Job file (if appropriate)
Job file 1:
```
job "test-2070-2" {
datacenters = ["dc1"]
group "test-2070-2" {

restart {
attempts=0
}
count=1
task "test-2070-2" {
driver = "podman"
config {
image = "image_with_gpu"
}
resources {
cpu = 2650
memory = 8192
device "nvidia/gpu" {
count = 2

constraint {
attribute = "${device.model}"
value = "NVIDIA GeForce RTX 2070 SUPER"
}

constraint {
attribute = "${device.ids}"
operator = "set_contains"
value = "GPU-9b5df054-6f08-f35c-9c4c-5709b19efea5,GPU-1846fc5f-8c71-bfab-00e1-9c190dd88ed7"
}

}
}
}
}
}
```

Job file 2:
```
job "test-2070-2" {
datacenters = ["dc1"]
group "test-2070-2" {

restart {
attempts=0
}
count=1
task "test-2070-2" {
driver = "podman"
config {
image = "image_with_gpu"
}
resources {
cpu = 2650
memory = 8192
device "nvidia/gpu" {
count = 1

constraint {
attribute = "${device.model}"
value = "NVIDIA GeForce RTX 2070 SUPER"
}

constraint {
attribute = "${device.ids}"
operator = "set_contains"
value = "GPU-9b5df054-6f08-f35c-9c4c-5709b19efea5"
}

}
}
}
}
}
```

Reproduce the behavior with the two GPU job files and the stated Nomad, nomad-driver-podman, and nomad-device-nvidia versions. Start by tracing device allocation and placement handling for UUID constraints, then identify the relevant scheduler or device-allocation tests. Done means a job requesting an already allocated GPU is rejected or reports the expected placement warning without disrupting valid allocations.

Written by the indexing model from the issue text.