Fix: [Actions] Ubuntu 18.04 by default has a compiler too old for OpenTTD (#9481)

.github/workflows/release.yml

@@ -373,14 +373,19 @@ jobs:
         include:
         - container_image: "ubuntu:18.04"
           bundle_name: "bionic"
+          compiler: "g++-8"
         - container_image: "ubuntu:20.04"
           bundle_name: "focal"
+          compiler: "g++"
         - container_image: "ubuntu:20.10"
           bundle_name: "groovy"
+          compiler: "g++"
         - container_image: "debian:buster"
           bundle_name: "buster"
+          compiler: "g++"
         - container_image: "debian:bullseye"
           bundle_name: "bullseye"
+          compiler: "g++"
 
     runs-on: ubuntu-20.04
     container:
@@ -406,7 +411,7 @@ jobs:
         apt-get install -y --no-install-recommends \
           cmake \
           debhelper \
-          g++ \
+          ${{ matrix.compiler }} \
           git \
           make \
           openssl \
@@ -432,7 +437,7 @@ jobs:
         cd build
 
         echo "::group::CMake"
-        cmake ${GITHUB_WORKSPACE} \
+        CXX=${{ matrix.compiler }} cmake ${GITHUB_WORKSPACE} \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
           -DCMAKE_INSTALL_PREFIX=/usr \
           # EOF