Fix using const char* and wxString in ternary operator

Using a const char* and a wxString in the two branches of the ternary
operator resulted in compile-time errors since the result type of the
conditional expression was ambiguous, so add explicit conversions to fix
it.

Closes https://github.com/wxWidgets/wxWidgets/pull/2634

See #19355.

samples/internat/internat.cpp

@@ -210,7 +210,7 @@ bool MyApp::OnInit()
         langInfo = wxLocale::GetLanguageInfo(wxLANGUAGE_DEFAULT);
     const wxString
         langDesc = langInfo ? langInfo->Description
-                            : "the default system locale";
+                            : wxString("the default system locale");
 
     if ( m_setLocale == Locale_Ask )
     {