[gtksourceview] tests: use Adwaita scheme by default

[Christian Hergert <chergert src gnome org>]

commit b89a3e95ebc389782247e6a2b1265d1d5b19ecd2
Author: Christian Hergert <chergert redhat com>
Date:   Mon Aug 9 11:15:02 2021 -0700

    tests: use Adwaita scheme by default

 tests/test-widget.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/tests/test-widget.c b/tests/test-widget.c
index ec00016c..2282772d 100644
--- a/tests/test-widget.c
+++ b/tests/test-widget.c
@@ -1061,6 +1061,7 @@ static void
 test_widget_init (TestWidget *self)
 {
        GtkSourceSpaceDrawer *space_drawer;
+       GtkSourceStyleScheme *style_scheme;
        GFile *file;
 
        self = test_widget_get_instance_private (self);
@@ -1120,6 +1121,11 @@ test_widget_init (TestWidget *self)
                                "style-scheme",
                                G_BINDING_SYNC_CREATE);
 
+       style_scheme = gtk_source_style_scheme_manager_get_scheme (
+               gtk_source_style_scheme_manager_get_default (),
+               "Adwaita");
+       gtk_source_buffer_set_style_scheme (self->buffer, style_scheme);
+
        g_object_bind_property (self->show_map_checkbutton,
                                "active",
                                self->map,