ci: Update Qt binaries for GitHub Actions

On 2019-12-09 Visual Studio has been upgraded to 16.4.0 in Windows
Server 2019 (windows-latest) virtual environment.

.github/workflows/ci.yml

@@ -7,8 +7,8 @@ jobs:
     runs-on: windows-latest
     env:
         PYTHONUTF8: 1
-        QT_DOWNLOAD_URL: 'https://github.com/sipsorcery/qt_win_binary/releases/download/v1.4/Qt5.9.8_x64_static_vs2019.zip'
-        QT_DOWNLOAD_HASH: 'f285cbb02bec3b3f3cc2621e3fa7d5edf0d6a66fa30c57859e583acda954ea80'
+        QT_DOWNLOAD_URL: 'https://github.com/sipsorcery/qt_win_binary/releases/download/v1.6/Qt5.9.8_x64_static_vs2019.zip'
+        QT_DOWNLOAD_HASH: '9a8c6eb20967873785057fdcd329a657c7f922b0af08c5fde105cc597dd37e21'
         QT_LOCAL_PATH: 'C:\Qt5.9.8_x64_static_vs2019'
         VCPKG_INSTALL_PATH: "$env:VCPKG_INSTALLATION_ROOT/installed"
         PLATFORM: x64