Discovered in the course of #878: On mobile Linux distros such as postmarketOS or Mobian GtkDialogs are automatically stretched to cover the screen. The add-podcast dialog currently expands the hbox with the text entry which looks a bit odd (and is also a bit superfluous because it still only shows a single line of input).

Using <property name="expand">False</property> in gpodderaddpodcast.ui makes it look like this.

The large amount of whitespace might still look a bit odd but the text entry and paste button seem more intuitive and usable to me this way.

I'm happy to submit a tiny pull request to fix this, if that would be appreciated.