CI: workaround for missing Node 20 in older containers

https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

.github/workflows/build.yml

@@ -221,10 +221,7 @@ jobs:
     container: ${{ matrix.container }}
 
     steps:
-      - name: Check if running in container
-        if: matrix.container != ''
-        run: echo "GHA_CONTAINER=${{ matrix.container }}" >> $GITHUB_ENV
-      - name: If running in container, upgrade packages
+      - name: Setup container environment
         if: matrix.container != ''
         run: |
           apt-get -o Acquire::Retries=3 update && DEBIAN_FRONTEND=noninteractive apt-get -y install tzdata && apt-get -o Acquire::Retries=3 install -y sudo software-properties-common wget curl apt-transport-https make apt-file sudo unzip libssl-dev build-essential autotools-dev autoconf automake g++ libc++-helpers python ruby cpio gcc-multilib g++-multilib pkgconf python3 ccache libpython-dev locales
@@ -239,6 +236,11 @@ jobs:
           sudo wget https://bootstrap.pypa.io/pip/$python_version/get-pip.py
           sudo python3 get-pip.py
           sudo /usr/local/bin/pip install cmake
+
+          if [[ "${{matrix.container}}" == "ubuntu:16.04" ]] || [[ "${{matrix.container}}" == "ubuntu:18.04" ]]; then
+            echo "ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true" >> $GITHUB_ENV
+          fi
+
       - uses: actions/checkout@v3
 
       - name: Install packages