Add permissions and fetch for PR validation

Update GitHub Actions workflow to include `issues: write` and `pull-requests: write` permissions, and fetch the base branch before comparing changes for more accurate dataset validation.

Author: kasumi-1

.github/workflows/validate-datasets.yml

@@ -18,6 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: read
+      issues: write
       pull-requests: write
 
     steps:
@@ -41,6 +42,7 @@ jobs:
       run: |
         if [ "${{ github.event_name }}" = "pull_request" ]; then
           # For PRs, compare against the base branch
+          git fetch origin "${{ github.base_ref }}" --depth=1
           git diff --name-only origin/${{ github.base_ref }}...HEAD | grep "^datasets/" | cut -d'/' -f1-2 | sort -u > changed_datasets.txt
         else
           # For pushes to master, check the last commit
@@ -127,7 +129,7 @@ jobs:
             console.log('Could not create comment:', error.message)
             console.log('This is likely due to permissions. The validation still failed - check the Actions tab for details.')
           }
-    
+
     - name: Comment on PR success
       if: success() && github.event_name == 'pull_request' && steps.changed-datasets.outputs.has_changes == 'true'
       uses: actions/github-script@v7