mypy: ignore enum argument type: UrlFormattingOption

The docs say:

> The options from QUrl::ComponentFormattingOptions are also possible.

> The FormattingOptions type is a typedef for QFlags<UrlFormattingOption>. It stores an OR combination of UrlFormattingOption values.

Maybe we should be should be definining out own types for some of the
enums that include both the QFlag, enum and any child enums.

qutebrowser/browser/browsertab.py

@@ -1322,7 +1322,8 @@ class AbstractTab(QWidget):
     def __repr__(self) -> str:
         try:
             qurl = self.url()
-            url = qurl.toDisplayString(QUrl.ComponentFormattingOption.EncodeUnicode)
+            as_unicode = QUrl.ComponentFormattingOption.EncodeUnicode
+            url = qurl.toDisplayString(as_unicode)  # type: ignore[arg-type]
         except (AttributeError, RuntimeError) as exc:
             url = '<{}>'.format(exc.__class__.__name__)
         else: