make github actions use gcc 12

.github/workflows/network.yml

@@ -29,13 +29,12 @@ jobs:
         uses: actions/checkout@v2
 
       - name: build
-        run: |
-          sudo apt update
-          sudo apt install gcc-12 g++-12
         env:
           CC: gcc-12
           CXX: g++-12
         run: |
+          sudo apt update
+          sudo apt install gcc-12 g++-12
           mkdir build
           cd build
           cmake ..