defaultvalue test needs updating whenever Adwaita changes
This test checks that the default value of the pspecs is the same as what we get out of
gtk_widget_style_get_property. If Adwaita overrides any values, then the test usually needs to be updated to not check this. It's a cumbersome process.
Let's consider if we can do better, like
- Is the test needed
- If so, should we use an "Empty" theme?
See !253 (merged) for a recent update.