bug#68512: Qutebrowser 3, no sound from pipewire-only system

[chris]

Possibly this was the change from Iyzsong which enabled sound here,
```sh
$ git diff fbbbc2088ce933d83f5b0be75308fdcb6b40fa57 
d9368572abd3683bed4263eb5e149bb404baee59 
diff --git a/gnu/packages/qt.scm b/gnu/packages/qt.scm
index 76e9e519c7..01327f6ccf 100644
--- a/gnu/packages/qt.scm
+++ b/gnu/packages/qt.scm
@@ -2708,7 +2708,8 @@ (define-public qtwebengine-5
                   "src/buildtools/config/linux.pri"
                   (lambda (in out)
                     (display (get-string-all in) out)
-                    (display "\ngn_args += use_system_openh264=true\n" out)))
+                    (display "\ngn_args += use_system_openh264=true\n" out)
+                    (display "\ngn_args += link_pulseaudio = true\n" out)))
                  ;; Qtwebengine is not installed into the same prefix as
                  ;; qtbase.  Some qtbase QTLibraryInfo constants will not
                  ;; work.  Replace with the full path to the qtwebengine-5
```

No equivalent is found by me in the qtwebengine definition that supplies 
qtwebgine 6