[GH Action] Upgrade Windows runner to windows-latest (#30)

Author: FlorianReimold

.github/workflows/build-windows.yml

@@ -24,7 +24,7 @@ jobs:
     # The CMake configure and build commands are platform agnostic and should work equally well on Windows or Mac.
     # You can convert this to a matrix build if you need cross-platform coverage.
     # See: https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/managing-complex-workflows#using-a-build-matrix
-    runs-on: windows-2019
+    runs-on: windows-latest
 
     steps:
 
@@ -62,7 +62,6 @@ jobs:
       # See https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html?highlight=cmake_build_type
       run: |
            cmake -B ${{github.workspace}}/_build `
-                 -G "Visual Studio 16 2019" `
                  -A ${{ matrix.build_arch }} `
                  -T ${{ env.VS_TOOLSET }} `
                  -DCMAKE_INSTALL_PREFIX=${{env.INSTALL_PREFIX}} `