Enable recursive submodule checkout in CI jobs

Updated the `actions/checkout@v4` step in both the `build-backend`
and `docker-build` jobs to include the `submodules: recursive`
option. This ensures that Git submodules are properly initialized
and updated during the CI workflow. These changes are critical
for projects that rely on submodules for external dependencies
or shared code.

Author: Timothy Dodd

.github/workflows/main.yml

@@ -15,10 +15,12 @@ jobs:
   build-backend:
     name: Build Backend
     runs-on: ubuntu-latest
-    
+
     steps:
     - name: Checkout repository
       uses: actions/checkout@v4
+      with:
+        submodules: recursive
 
     - name: Setup .NET
       uses: actions/setup-dotnet@v4
@@ -73,10 +75,12 @@ jobs:
     runs-on: ubuntu-latest
     needs: [build-backend, build-frontend]
     if: github.event_name == 'push' && (github.ref == 'refs/heads/master' || github.ref == 'refs/heads/main')
-    
+
     steps:
     - name: Checkout repository
       uses: actions/checkout@v4
+      with:
+        submodules: recursive
 
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3