Motivation for this change

RStudio failed to build after fe0ab94 (pr #31357)

part of build log:

CMake Error at /nix/store/dz9488m52zgf8p36q9qji5xga50pbisd-qt-5.9.1/lib/cmake/Qt5Gui/Qt5GuiConfig.cmake:13 (message):
  The imported target "Qt5::Gui" references the file

     "/nix/store/1m2paiq8z7g9vz3gykw44yimqb6v6109-qtbase-5.9.1-bin/lib/qt-5.9/plugins/imageformats/libqicns.so"

  but this file does not exist.  Possible reasons include:

  * The file was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and contained

     "/nix/store/dz9488m52zgf8p36q9qji5xga50pbisd-qt-5.9.1/lib/cmake/Qt5Gui/Qt5Gui_QICNSPlugin.cmake"

  but not all the files it references.

The log says it cannot find libqicns.so, which is a library provided by qtimageformats.

I guess the error is caused by the incorrect way to specify qt dependencies, this commit fixes it.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.