Clang warnings (last one)

```
 [91%] Building CXX object CMakeFiles/lxqt.dir/lxqtrotatedwidget.cpp.o
/tmp/makepkg/liblxqt-git/src/liblxqt/lxqtapplication.cpp:69:50: warning: lambda capture 'this' is not used [-Wunused-lambda-capture]
   69 |         connect(this, &Application::unixSignal, [this, signo_list] (int signo)
      |                                                  ^~~~~
1 warning generated.           
```