String literal template escape not working `%%{`

### Nomad version
Nomad v1.4.1 (2aa7e66bdb526e25f59883952d74dad7ea9a014e)

### Operating system and Environment details
Ubuntu 20.04

### Issue
Template escape sequence to allow putting a literal `%{` in an argument does not work.

### Reproduction steps
Run nomad agent with `sudo nomad agent -dev`
`nomad job run ` (see job file below)

Check the status of the job/allocation and see the error:
```
* failed to parse config:
* Invalid template control keyword: "test" is not a valid template control keyword.
```

#### Expected Result
Job runs successfully and echos `%{test}`

#### Actual Result
Job fails with:
```
* failed to parse config:
* Invalid template control keyword: "test" is not a valid template control keyword.
```

### Job file (if appropriate)
```
job "template-test" {
datacenters = ["dc1"]
group "processors" {
count = 1
task "echotest" {
driver = "exec"
config {
command = "/usr/bin/echo"
args = [
"%%{test}"
]
}
}
}
}
```

### Nomad Server logs (if appropriate)
```
2022-10-19T15:05:17.390-0700 [ERROR] client.alloc_runner.task_runner: running driver failed: alloc_id=117f823f-182e-5cd7-1441-708882dd5cae task=echotest
error=
| 2 errors occurred:
| \t* failed to parse config:
| \t* Invalid template control keyword: "test" is not a valid template control keyword.
|

2022-10-19T15:05:17.391-0700 [INFO] client.alloc_runner.task_runner: not restarting task: alloc_id=117f823f-182e-5cd7-1441-708882dd5cae task=echotest reason="Error was unrecoverable"
```

### Nomad Client logs (if appropriate)
N/A

Reproduce the issue with `sudo nomad agent -dev` and the supplied job file, then trace Nomad's template parsing for the `%%{` escape in the `args` value. Done means the job runs successfully and echoes the literal `%{test}` without the invalid template control keyword error.

Written by the indexing model from the issue text.