Typo fixes.

manual tests/6 qt4/main.cpp

@@ -12,7 +12,7 @@ int main(int argc, char **argv) {
   if(qi2.width() != 640) {
       return 1;
   }
-  win->setWindowTitle("Meson Qt5 build test");
+  win->setWindowTitle("Meson Qt4 build test");
 
   win->show();
   return app.exec();

manual tests/6 qt4/meson.build

@@ -1,4 +1,4 @@
-project('qt5 build test', 'cpp')
+project('qt4 build test', 'cpp')
 
 # This is a manual test rather than an automatic one
 # because during Debian package builds only Qt4 or Qt5