fix windows per actions/runner-images#2667

.github/workflows/windows.yml

@@ -12,11 +12,17 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
+    - name: boost
+      run: |
+        # Use the boost_1_72_0-msvc-14.1-64.exe for Windows 2016
+        $Url = "https://sourceforge.net/projects/boost/files/boost-binaries/1.72.0/boost_1_72_0-msvc-14.2-64.exe"
+        (New-Object System.Net.WebClient).DownloadFile($Url, "$env:TEMP\boost.exe")
+        Start-Process -Wait -FilePath "$env:TEMP\boost.exe" "/SILENT","/SP-","/SUPPRESSMSGBOXES","/DIR=C:\hostedtoolcache\windows\Boost\1.72.0\x86_64"
     - name: cmake
       run: |
         cmake -E make_directory build
         cd build
-        cmake -DBOOST_ROOT="${env:BOOST_ROOT_1_72_0}" ..
+        cmake -DBOOST_ROOT="C:\hostedtoolcache\windows\Boost\1.72.0" ..
     - name: Compile
       working-directory: build
       run: cmake --build . -j2