GHA: Fix ownership of repo in container

Avoid:
> fatal: detected dubious ownership in repository at '/__w/turtle/turtle'

by adding that path to the git `safe.path`.
This is caused by the command(s) running inside the container but the
folder being created outside the container so the owner inside the container is not what is expected by git.

.github/workflows/ci.yml

@@ -75,6 +75,7 @@ jobs:
             apt-get -o Acquire::Retries=$NET_RETRY_COUNT update
             apt-get -o Acquire::Retries=$NET_RETRY_COUNT install -y g++ git cmake
             git config --global pack.threads 0
+            git config --global --add safe.directory "$GITHUB_WORKSPACE"  # Avoid ownership issues of repo in container
 
       - uses: actions/checkout@v4
         with: