try fech all in submodules

Author: hjwp

.github/workflows/tests.yml

@@ -36,6 +36,14 @@ jobs:
             -t hjwp/obeythetestinggoat-book-tester:latest \
             bash -c "cat ~/.gitconfig"
 
+      - name: fetch submodule branches
+        run: |
+          docker run --rm \
+            --mount type=volume,source=rootmount,target=/root \
+            --mount type=bind,source=./,target=/app \
+            -t hjwp/obeythetestinggoat-book-tester:latest \
+            bash -c "git submodule foreach 'git fetch --all'"
+
       - name: check submodule branches
         run: |
           docker run --rm \