CI: Avoid "set-env" in github Linux CI workflow

Author: jgriffiths

.github/workflows/ci-linux.yaml

@@ -47,6 +47,15 @@ jobs:
         with:
           python-version: 3.8
 
+      - name: Set env vars
+        run: |
+          echo "CC=${{ matrix.compiler }}-${{ matrix.version }}" >> $GITHUB_ENV
+          if [ "${{ matrix.compiler }}" == "clang" ]; then
+              echo "CXX=clang++-${{ matrix.version }}" >> $GITHUB_ENV
+          else
+              echo "CXX=g++-${{ matrix.version }}" >> $GITHUB_ENV
+          fi
+
       - name: Install
         run: |
           python -m pip install cmake==3.17.3 conan==1.28.1 --upgrade
@@ -57,12 +66,8 @@ jobs:
 
           if [ "${{ matrix.compiler }}" = "gcc" ]; then
             sudo apt-get install -y g++-${{ matrix.version }} g++-${{ matrix.version }}-multilib
-            echo "::set-env name=CC::gcc-${{ matrix.version }}"
-            echo "::set-env name=CXX::g++-${{ matrix.version }}"
           else
             sudo apt-get install -y clang-${{ matrix.version }} clang-tidy-${{ matrix.version }} g++-multilib
-            echo "::set-env name=CC::clang-${{ matrix.version }}"
-            echo "::set-env name=CXX::clang++-${{ matrix.version }}"
           fi
 
       - name: Install dependencies (system)