Handle PyQt WebEngine version strings being Optional

With PyQt6-WebEngine 6.6.0 some pointer return types are now wrapped in
Optionals[]. In practice they should never be None, we've been relying on them
being set for long enough.

`qWebEngineVersion()` and `qWebEngineChromiumVersion()` now are typed as
returning `Optional[str]`. In `from_api()` we can handle the
`chromium_version` being null, so pass that through, but we are depending on
the `qtwe_version` being set, so add an assert there.

ref: qutebrowser#7990

Author: toofar

qutebrowser/utils/version.py

@@ -686,7 +686,7 @@ def _infer_chromium_version(
         return cls._CHROMIUM_VERSIONS.get(minor_version)
 
     @classmethod
-    def from_api(cls, qtwe_version: str, chromium_version: str) -> 'WebEngineVersions':
+    def from_api(cls, qtwe_version: str, chromium_version: Optional[str]) -> 'WebEngineVersions':
         """Get the versions based on the exact versions.
 
         This is called if we have proper APIs to get the versions easily
@@ -796,8 +796,10 @@ def qtwebengine_versions(*, avoid_init: bool = False) -> WebEngineVersions:
         except ImportError:
             pass  # Needs QtWebEngine 6.2+ with PyQtWebEngine 6.3.1+
         else:
+            qtwe_version = qWebEngineVersion()
+            assert qtwe_version is not None
             return WebEngineVersions.from_api(
-                qtwe_version=qWebEngineVersion(),
+                qtwe_version=qtwe_version,
                 chromium_version=qWebEngineChromiumVersion(),
             )