chore(workflows): fix undesirable workflows git (#31912)

.github/workflows/undesirable-test-additions.yaml

@@ -15,17 +15,14 @@ jobs:
           fetch-depth: 0 # Fetch all history for comparison
           sparse-checkout: true
           ref: ${{ github.event.pull_request.head.ref }}
+          repository: ${{ github.event.pull_request.head.repo.full_name }}
       - name: Check for undesirable code
         run: |
           #!/bin/bash
           set -e
 
-          echo "### Fetching base branch for comparison..."
-          git fetch origin ${{ github.event.pull_request.base.ref }}
-
-          BASE_BRANCH=origin/${{ github.event.pull_request.base.ref }}
+          BASE_BRANCH=${{ github.event.pull_request.base.ref }}
           echo "Base branch is: $BASE_BRANCH"
-          echo "Current HEAD is: $(git rev-parse HEAD)"
           BASE_BRANCH_REF=${{ github.event.pull_request.base.sha }}
           echo "Base branch ref for this PR is: $BASE_BRANCH_REF"
 
@@ -44,7 +41,7 @@ jobs:
           fi
 
           echo "### Calculating file changes in '__fixtures__' directories..."
-          git diff --name-status $BASE_BRANCH..HEAD > diff_name_status.txt
+          git diff --name-status $BASE_BRANCH_REF > diff_name_status.txt
 
           echo "### Processing added files in '__fixtures__' directories..."
           ADDED_FIXTURES=$(grep '^A' diff_name_status.txt | awk '{print $2}' | grep '/__fixtures__/' || true)