Fixes windows CI by using the valid virtual environments `windows-2019`

The virtual-environments documents are at: https://github.com/actions/virtual-environments .
Currently, the `windows-latest` == `windows-2022`

We currently are using `Microsoft Visual Studio\2019` installed with `windows-2019` and that not installed in `windows-2022`

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>

.github/workflows/main.yml

@@ -42,7 +42,7 @@ jobs:
 
   winbuild:
     name: Windows Build
-    runs-on: windows-latest
+    runs-on: windows-2019
     strategy:
       fail-fast: false
       matrix:
@@ -63,6 +63,7 @@ jobs:
         run: choco install ninja
       - name: Build
         shell: cmd
+        # vcvarsall.bat need explicit Visual Studio 2019 to be installed
         run: |
           set "HOME=%CD%"
           set CL_ARCH=${{ fromJson('{ "x86": "amd64_x86", "x64": "amd64" }')[matrix.arch] }}