[CI] Fix failing Windows Python 3.10 tests

A recent dependency change caused the tests running on GitHub Actions
under Python 3.10.5 on Windows to fail when starting pytest run:

    ...
    INTERNALERROR>   File "<frozen importlib._bootstrap>", line 123, in acquire
    INTERNALERROR> KeyError: xxxx

The cause seems to have been a newer version of chardet package released
recently.

* Fixed by pinning chardet to v4
* Also pin Windows version to 2019 to match packaging workflow

See-also: https://github.com/deluge-torrent/deluge/actions/runs/2578427588
Issue: https://github.com/chardet/chardet/issues/265

.github/workflows/ci.yml

@@ -65,7 +65,7 @@ jobs:
           path: /cores
 
   test-windows:
-    runs-on: windows-latest
+    runs-on: windows-2019
     strategy:
       matrix:
         python-version: ["3.7", "3.10"]

requirements.txt

@@ -6,7 +6,7 @@ pyxdg
 pillow
 mako
 setuptools
-chardet
+chardet==4.0.0
 setproctitle
 pywin32; sys_platform == 'win32'
 certifi; sys_platform == 'win32'