Ensure tests have default-initialized settings (#4498)

Also rework HighlightController test directory creation/saving to ensure the test directory is written to & cleaned up appropriately

tests/src/main.cpp

@@ -4,6 +4,7 @@
 #include "common/Outcome.hpp"
 #include "common/QLogging.hpp"
 #include "providers/twitch/api/Helix.hpp"
+#include "singletons/Settings.hpp"
 
 #include <gtest/gtest.h>
 #include <QApplication>
@@ -27,6 +28,9 @@ int main(int argc, char **argv)
 
     chatterino::NetworkManager::init();
 
+    // Ensure settings are initialized before any tests are run
+    chatterino::Settings settings("/tmp/c2-empty-test");
+
     QtConcurrent::run([&app] {
         auto res = RUN_ALL_TESTS();