Double-check that default gcc version is correct

.github/workflows/ci.yml

@@ -13,6 +13,7 @@ env:
   VCPKG_ROOT: "vcpkg"
   VCPKG_BINARY_SOURCES: "clear;nuget,GitHub,readwrite"
   LINUX_RUNNER: ubuntu-22.04
+  DEFAULT_UBUNTU_GCC_VERSION: 11 # update this if you change LINUX_RUNNER
   WINDOWS_RUNNER: windows-2022
 
 jobs:
@@ -56,6 +57,10 @@ jobs:
           sudo apt upgrade -y
           sudo apt install --no-install-recommends build-essential libtbb-dev ninja-build doxygen graphviz
 
+          # Double check that the default version is what we think it is
+          GCC_MAJOR_VER=`gcc -dumpversion|sed -E 's/^([0-9]+)\./.*$\1/'`
+          test $GCC_MAJOR_VER -eq $DEFAULT_UBUNTU_GCC_VERSION
+
       - name: Install clang (Linux)
         if: matrix.platform == 'linux' && matrix.compiler == 'clang'
         run: |