Remove test-data submodule from template, keep instructions

.github/workflows/ctest.yml

@@ -45,10 +45,9 @@ jobs:
     - name: Checkout repository
       uses: actions/checkout@v4
 
-    - name: Clone required submodules # TODO-TEMPLATE: Check required submodules and update if needed
+    - name: Clone required submodules # TODO-TEMPLATE: Add test-data submodule here, if needed
       run: |
         git submodule init extern/googletest
-        git submodule init extern/test-data
         git submodule update
 
     - name: Install CMake