build: pin Windows GitHub runner to windows-2019

GitHub is removing the Windows 2016 runner image on March 15, 2022.

Refs: https://github.blog/changelog/2021-10-19-github-actions-the-windows-2016-runner-image-will-be-removed-from-github-hosted-runners-on-march-15-2022/

PR-URL: #42349
Reviewed-By: Mestery <mestery@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: richardlau

Diff for: .github/workflows/build-windows.yml

@@ -8,7 +8,7 @@ env:
 
 jobs:
   build-windows:
-    runs-on: windows-2016
+    runs-on: windows-2019
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python ${{ env.PYTHON_VERSION }}