Update bookworm backport to 5.15.15+dfsg-3

Soren Stoutnerrequested to merge
soren/qtwebengine:new-bookworm-backport into bookworm-backports

I have tested all the browsers (Angelfish, Falkon, Konqueror, morph-browser, qutebrowser, and Privacy Browser) on a system running bookworm, including testing download with Anglefish.

Merge request reports