refactor(Qt): fix build with Qt 5.15 again

A deprecated function was previously replaced with an overload that
also got recently deprecated [1].

1. https://code.qt.io/cgit/qt/qtbase.git/commit/?h=5.15&id=46ebd11e

(cherry picked from commit 6a59f0fe4d)

src/widget/form/searchsettingsform.cpp

@@ -38,7 +38,7 @@ SearchSettingsForm::SearchSettingsForm(QWidget *parent) :
     reloadTheme();
 
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
-    connect(ui->startSearchComboBox, QOverload<int, const QString &>::of(&QComboBox::currentIndexChanged),
+    connect(ui->startSearchComboBox, QOverload<int>::of(&QComboBox::currentIndexChanged),
 #else
     connect(ui->startSearchComboBox, static_cast<void(QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
 #endif