Set env for nightly job. (#1651)

.github/workflows/nightly.yml

@@ -88,12 +88,12 @@ jobs:
 
             if [ "${{ matrix.compiler }}" = "gcc" ]; then
               sudo apt-get install -y g++-${{ matrix.version }}
-              echo "::set-env name=CC::gcc-${{ matrix.version }}"
-              echo "::set-env name=CXX::g++-${{ matrix.version }}"
+              echo "CC=gcc-${{ matrix.version }}" >> $GITHUB_ENV
+              echo "CXX=g++-${{ matrix.version }}" >> $GITHUB_ENV
             else
               sudo apt-get install -y clang-${{ matrix.version }}
-              echo "::set-env name=CC::clang-${{ matrix.version }}"
-              echo "::set-env name=CXX::clang++-${{ matrix.version }}"
+              echo "CC=clang-${{ matrix.version }}" >> $GITHUB_ENV
+              echo "CXX=clang++-${{ matrix.version }}" >> $GITHUB_ENV
             fi
 
             sudo apt-get install \