toTOML incorrectly renders nested tables.

When using toTOML function when rendering secrets that were stored in vault when transforming the map to TOML it incorrectly renders the nested tables.

Take this as example.

The original data stored in vault:
```
{
"metrics": {
"prometheus": {
"enabled": true
}
}
}
```

Using this template:
```
{{ with secret "secrets/staging/service.toml" -}}
{{ .Data.data | toTOML }}
{{- end }}
```

Renders:
```
[metrics]
[metrics.prometheus]
enabled = true
```

The spec for TOML states that nested tables should be [x.y] I don't understand what's the problem.

Start by locating the toTOML template function and reproduce the nested-table example from the issue. Compare its rendered output with the TOML specification and establish the expected nesting syntax; done means the example renders valid nested tables without changing unrelated output.

Written by the indexing model from the issue text.