fix Debian CI (#1946)

.github/workflows/coq-debian.yml

@@ -37,6 +37,8 @@ jobs:
     - uses: actions/checkout@v4
       with:
         submodules: recursive
+    - name: work around broken git config
+      run: git config --global --add safe.directory "*"
     - name: container build params
       run: etc/ci/describe-system-config.sh
     - name: make deps