cmake: Fix cmake option display

When editing a multiple choice cmake option the
background ( the text of the current value )
would shine through. This fixes that by setting
setAutoFillBackground(true) on the editor widget

Change-Id: Ie36ea13f2d0532c375f22a33569772c3b2c604fb
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/cmakeprojectmanager/configmodelitemdelegate.cpp

@@ -64,6 +64,7 @@ QWidget *ConfigModelItemDelegate::createEditor(QWidget *parent, const QStyleOpti
             auto edit = new QComboBox(parent);
             edit->setAttribute(Qt::WA_MacSmallSize);
             edit->setFocusPolicy(Qt::StrongFocus);
+            edit->setAutoFillBackground(true);
             for (const QString &s : qAsConst(data.values))
                 edit->addItem(s);
             return edit;