version_checker: don't delete network reply in finished handler

The Qt docs warn against deleting a QNetworkReply while the
`finished` handler is running (https://doc.qt.io/qt-6/qnetworkreply.html).

We're not explicitly deleting it here, just setting the Python reference
to `None`, but that might be enough to cause the object to be
destroyed, explaining the crash we're seeing on Windows.

Instead we set the option on QNetworkAccessManager to auto-delete
replies.

src/main/python/main/ayab/version_checker.py

@@ -25,6 +25,7 @@ def start_background_check(self) -> None:
         latest_relase_url = f"https://api.github.com/repos/{self.REPO}/releases/latest"
         self.logger.debug("Getting %s", latest_relase_url)
         self._network_manager = QNetworkAccessManager()
+        self._network_manager.setAutoDeleteReplies(True)
         self._version_check_reply = self._network_manager.get(
             QNetworkRequest(latest_relase_url)
         )
@@ -96,5 +97,4 @@ def version_check_finished(self) -> None:
         finally:
             # make sure to free resources once done
             self.logger.debug("Cleaning up")
-            self._version_check_reply = None
             self._network_manager = None