fix(ci): Use merge-base for correct target validation

The validation workflow was comparing changes against the wrong base,
causing incorrect target detection when PR branches get out of sync.

Now it uses git merge-base to find where the branch actually split off,
so it only validates the targets that were actually changed in the PR.

This is the same fix as sherlock-project#2588 in the upstream repo.

Author: dollaransh17

.github/workflows/validate_modified_targets.yml

@@ -14,32 +14,39 @@ jobs:
       contents: read
       pull-requests: write
     steps:
-      - name: Checkout repository
+      - name: Checkout PR branch
         uses: actions/checkout@v5
         with:
-          ref: ${{ github.base_ref }}
-          fetch-depth: 1
+          # Check out the actual PR code, not the base branch
+          ref: ${{ github.event.pull_request.head.sha }}
+          # Fetch all history so we can find the common ancestor (merge-base)
+          fetch-depth: 0
 
       - name: Set up Python
         uses: actions/setup-python@v6
         with:
-          python-version: '3.13'
+          python-version: "3.13"
 
       - name: Install Poetry
         uses: abatilo/actions-poetry@v4
         with:
-          poetry-version: 'latest'
+          poetry-version: "latest"
 
       - name: Install dependencies
         run: |
           poetry install --no-interaction --with dev
 
-      - name: Drop in place updated manifest from base
+      - name: Prepare JSON versions for comparison
         run: |
-          cp sherlock_project/resources/data.json data.json.base
-          git fetch origin pull/${{ github.event.pull_request.number }}/head:pr --depth=1
-          git show pr:sherlock_project/resources/data.json > sherlock_project/resources/data.json
+          # Fetch the target branch to ensure we can compare against it
+          git fetch origin ${{ github.base_ref }}
+          # Find the exact commit where this branch split from the target branch
+          MERGE_BASE=$(git merge-base origin/${{ github.base_ref }} HEAD)
+          echo "Comparing HEAD against merge-base commit: $MERGE_BASE"
+          # Copy the version of the file from the current PR branch (HEAD)
           cp sherlock_project/resources/data.json data.json.head
+          # Extract the version of the file from the merge-base commit
+          git show $MERGE_BASE:sherlock_project/resources/data.json > data.json.base
 
       - name: Discover modified targets
         id: discover-modified