[snap] Snapshot timestamp format doesn't honor user's prefered locale when in a snap

When running locally, the locale is properly used when formatting a snapshot's timestamp:

```
$ echo $LC_TIME
pt_PT.UTF-8
$ multipass info alive-chamois.snapshot2 | grep Created
Created: ter 14 nov 2023 16:04:17 WET
```

This is not the case when running in a snap

```
$ echo $LC_TIME
pt_PT.UTF-8
$ multipass info primary.snapshot1 | grep Created
Created: Tue Nov 14 14:35:27 2023 WET
```

Reproduce the difference between local and snap execution with LC_TIME=pt_PT.UTF-8 using the documented multipass info commands. Trace how the snap invocation formats the snapshot Created timestamp, then verify that the output honors the user's locale while preserving the existing timestamp information.

Written by the indexing model from the issue text.