Hide QtWebKit image format warning

This was hidden for tests in c390c797b2
but should be hidden for normal usage as well.

pytest.ini

@@ -36,6 +36,5 @@ qt_log_ignore =
     ^Geoclue error: Process org\.freedesktop\.Geoclue\.Master exited with status 127
     ^QObject::connect: Cannot connect \(null\)::stateChanged\(QNetworkSession::State\) to QNetworkReplyHttpImpl::_q_networkSessionStateChanged\(QNetworkSession::State\)
     ^QXcbClipboard: Cannot transfer data, no data available
-    ^Image of format '' blocked because it is not considered safe. If you are sure it is safe to do so, you can white-list the format by setting the environment variable QTWEBKIT_IMAGEFORMAT_WHITELIST=
 qt_wait_signal_raising = true
 xfail_strict = true

qutebrowser/utils/log.py

@@ -316,6 +316,10 @@ def qt_message_handler(msg_type, context, msg):
             'QNetworkSession::State) to '
             'QNetworkReplyHttpImpl::_q_networkSessionStateChanged('
             'QNetworkSession::State)',
+        # https://bugreports.qt.io/browse/QTBUG-53989
+        "Image of format '' blocked because it is not considered safe. If you "
+            "are sure it is safe to do so, you can white-list the format by "
+            "setting the environment variable QTWEBKIT_IMAGEFORMAT_WHITELIST=",
     ]
     if sys.platform == 'darwin':
         suppressed_msgs += [