Pass through Ctrl+Mousewheel in passthrough mode

See #3836

doc/changelog.asciidoc

@@ -66,6 +66,8 @@ Changed
 - The `content.autoplay` setting now supports URL patterns on Qt >= 5.11.
 - The `content.host_blocking.whitelist` setting now takes a list of URL
   patterns instead of globs.
+- In passthrough mode, Ctrl + Mousewheel now also gets passed through to the
+  page instead of zooming.
 
 Fixed
 ~~~~~

qutebrowser/browser/mouse.py

@@ -141,6 +141,10 @@ class MouseEventFilter(QObject):
             return True
 
         if e.modifiers() & Qt.ControlModifier:
+            mode = modeman.instance(self._tab.win_id).mode
+            if mode == usertypes.KeyMode.passthrough:
+                return False
+
             divider = config.val.zoom.mouse_divider
             if divider == 0:
                 return False