HeaderLabel: Too wide paddings when using in Gtk.ListBoxRow

### What Happened?

Originally from https://github.com/elementary/settings-applications/pull/268#discussion_r2632882081

Using Granite.HeaderLabel in Gtk.ListBoxRow introduces unnecessarily wide paddings (see the left pane):

c.f. using Gtk.Label in Gtk.ListBoxRow does not:

### Steps to Reproduce

See the screenshots above.

### Expected Behavior

Paddings should be decent even when used in Gtk.ListBoxRow.

### OS Version

8.x (Circe)

### OS Architecture

arm64 (on Raspberry Pi, Apple Silicon, etc.)

### Session Type

Secure Session (Wayland, This is the default)

### Software Version

Compiled from git

### Log Output

```shell

```

### Hardware Info

_No response_