fix github action

Author: huangminghuang

.github/workflows/main.yml

@@ -15,7 +15,7 @@ jobs:
         run: sudo apt-get install libboost-all-dev
       - name: Set Boost on Windows
         if: matrix.os == 'windows-latest' 
-        run:  echo "::set-env name=BOOST_ROOT::$env:BOOST_ROOT_1_72_0"
+        run:  echo ("BOOST_ROOT=" + $env:BOOST_ROOT_1_72_0) >> $env:GITHUB_ENV
       - name: install Boost on MacOS
         if: matrix.os == 'macos-latest'
         run: brew install boost