`humanize_list` accepts any value that can be coerced to a string for the last list item

### Bug Description

This should raise a TypeError but it doesn't:

```
>>> craft_cli.utils.humanize_list(['1', 2])
'1, and 2'
```

While this isn't exactly a big deal, it is an unexpected success that can mislead developers.

### To Reproduce

```
craft_cli.utils.humanize_list(['1', 2])
```

### part yaml

```shell

```

### Relevant log output

```shell
n/a
```