language_for_testing: Fix GetLocales namespace

test/language_for_testing.cpp

@@ -8,4 +8,7 @@ void LanguageInitialize() { }
 std::string_view LanguageTranslate(const char *key) { return key; }
 std::string_view LanguagePluralTranslate(const char *singular, std::string_view plural, int count) { return count == 1 ? singular : plural; }
 std::string_view LanguageParticularTranslate(std::string_view context, std::string_view message) { return message; }
+
+namespace devilution {
 std::vector<std::string> GetLocales() { return {}; }
+} // namespace devilution