Remove submodule and prevent future submodule additions (GoogleCloudPlatform#11846)

Author: melinath

.github/workflows/disallow-submodules.yml

@@ -0,0 +1,22 @@
+name: "Disallow submodules"
+permissions: read-all
+
+on:
+  pull_request
+
+jobs:
+  disallow-submodules:
+    runs-on: ubuntu-22.04
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.2
+    - name: Check for submodules
+      run: |
+        output=$(git submodule status --recursive 2>&1)
+        if [ ! -z $output ]; then
+          echo $output
+          echo "Submodules are not allowed"
+          exit 1
+        else
+          echo "No submodules found"
+        fi

.github/workflows/repository-documentation-deploy.yml

@@ -15,7 +15,7 @@ jobs:
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.2
         with:
-          submodules: true  # Fetch Hugo themes (true OR recursive)
+          submodules: false  # Fetch Hugo themes (true OR recursive)
           fetch-depth: 0    # Fetch all history for .GitInfo and .Lastmod
 
       - name: Setup Hugo

.github/workflows/repository-documentation-test.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.2
         with:
-          submodules: true  # Fetch Hugo themes (true OR recursive)
+          submodules: false  # Fetch Hugo themes (true OR recursive)
           fetch-depth: 0    # Fetch all history for .GitInfo and .Lastmod
 
       - name: Setup Hugo