Fixes #78642
This commit adds pyqtwebengine.

Motivation for this change

Without pyqtwebengine, when you try to view an ebook, you get the following error

Traceback (most recent call last):
  File "/nix/store/1zqhszwa961qf3nciz5wv854sfff18ph-calibre-4.8.0/bin/.calibre-parallel-wrapped", line 20, in <module>
    sys.exit(main())
  File "/nix/store/1zqhszwa961qf3nciz5wv854sfff18ph-calibre-4.8.0/lib/calibre/calibre/utils/ipc/worker.py", line 209, in main
    result = func(*args, **kwargs)
  File "/nix/store/1zqhszwa961qf3nciz5wv854sfff18ph-calibre-4.8.0/lib/calibre/calibre/gui_launch.py", line 80, in ebook_viewer
    from calibre.gui2.viewer.main import main
  File "/nix/store/1zqhszwa961qf3nciz5wv854sfff18ph-calibre-4.8.0/lib/calibre/calibre/gui2/viewer/main.py", line 12, in <module>
    from PyQt5.QtWebEngineCore import QWebEngineUrlScheme
ImportError: No module named QtWebEngineCore

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)

• 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 nixpkgs-review --run "nixpkgs-review wip"

• Tested execution of all binary files (usually in ./result/bin/)

• Determined the impact on package closure size (by running nix path-info -S before and after)

• Ensured that relevant documentation is up to date

• Fits CONTRIBUTING.md.