Adjust :debug-webaction for new-style enums

With scoped enums, we don't need to check whether the member belongs to the enum
class anymore, we just get it directly from there.

Also needed for PyQt 6 because we can't access the members unscoped anymore.

TODO: Pick to master?

qutebrowser/browser/browsertab.py

@@ -153,7 +153,6 @@ class AbstractAction:
 
     """Attribute ``action`` of AbstractTab for Qt WebActions."""
 
-    action_class: Type[Union['QWebPage', 'QWebEnginePage']]
     action_base: Type[Union['QWebPage.WebAction', 'QWebEnginePage.WebAction']]
 
     def __init__(self, tab: 'AbstractTab') -> None:
@@ -170,10 +169,10 @@ class AbstractAction:
 
     def run_string(self, name: str) -> None:
         """Run a webaction based on its name."""
-        member = getattr(self.action_class, name, None)
-        if not isinstance(member, self.action_base):
-            raise WebTabError("{} is not a valid web action!".format(name))
-        assert member is not None  # for mypy
+        try:
+            member = getattr(self.action_base, name)
+        except AttributeError:
+            raise WebTabError(f"{name} is not a valid web action!")
         self._widget.triggerPageAction(member)
 
     def show_source(self, pygments: bool = False) -> None:

qutebrowser/browser/webengine/webenginetab.py

@@ -59,8 +59,6 @@ class WebEngineAction(browsertab.AbstractAction):
     """QtWebEngine implementations related to web actions."""
 
     _widget: webview.WebEngineView
-
-    action_class = QWebEnginePage
     action_base = QWebEnginePage.WebAction
 
     def exit_fullscreen(self):

qutebrowser/browser/webkit/webkittab.py

@@ -44,7 +44,6 @@ class WebKitAction(browsertab.AbstractAction):
 
     """QtWebKit implementations related to web actions."""
 
-    action_class = QWebPage
     action_base = QWebPage.WebAction
 
     _widget: webview.WebView