mypy: Fix inspector typing

The previous solution with making AbstractInspector know about the concrete
inspector types results in Liskov issues for the backend-specific overrides:
https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides

So, for now, let's just declare them as Any. Perhaps we should have a
typing.Protocol to unify the two, as they don't share a common base class.
See #7098.

qutebrowser/browser/inspector.py

@@ -22,7 +22,7 @@
 import base64
 import binascii
 import enum
-from typing import cast, Optional, Union, TYPE_CHECKING
+from typing import cast, Optional, Any, TYPE_CHECKING
 
 from PyQt5.QtWidgets import QWidget
 from PyQt5.QtCore import pyqtSignal, pyqtSlot, QObject, QEvent
@@ -34,13 +34,9 @@ from qutebrowser.utils import log, usertypes
 from qutebrowser.keyinput import modeman
 from qutebrowser.misc import miscwidgets
 
-if TYPE_CHECKING:
-    from PyQt5.QtWebKitWidgets import QWebInspector, QWebPage
-    from PyQt5.QtWebEngineWidgets import QWebEnginePage
-    from qutebrowser.browser.webengine import webengineinspector
 
-
-_WidgetType = Union["QWebInspector", "webengineinspector.WebEngineInspectorView"]
+# FIXME:mypy How to annotate this properly without running into Liskov issues?
+_WidgetType = Any
 
 
 class Position(enum.Enum):
@@ -206,7 +202,8 @@ class AbstractWebInspector(QWidget):
         geom = base64.b64encode(data).decode('ASCII')
         configfiles.state['inspector']['window'] = geom
 
-    def inspect(self, page: Union["QWebPage", "QWebEnginePage"]) -> None:
+    # FIXME:mypy How to annotate 'page' properly without running into Liskov issues?
+    def inspect(self, page: Any) -> None:
         """Inspect the given QWeb(Engine)Page."""
         raise NotImplementedError
 

qutebrowser/browser/webkit/webkitinspector.py

@@ -31,8 +31,6 @@ class WebKitInspector(inspector.AbstractWebInspector):
 
     """A web inspector for QtWebKit."""
 
-    _widget = QWebInspector
-
     def __init__(self, splitter: miscwidgets.InspectorSplitter,
                  win_id: int,
                  parent: QWidget = None) -> None: