replace abandoned action with git diff

Author: alistairewj

.github/workflows/lint_sqlfluff.yml

@@ -9,27 +9,24 @@ jobs:
     steps:
       - name: checkout
         uses: actions/checkout@v4
+        with:
+          # Full history so we can diff the PR branch against its base
+          fetch-depth: 0
       - name: Install Python
         uses: actions/setup-python@v5
         with:
           python-version: "3.12"
       - name: install sqlfluff
         run: "pip install sqlfluff==4.1.0"
-      - name: Get changed files
-        id: get_file_changes
-        uses: trilom/file-changes-action@v1.2.4
-        with:
-          output: ' '
       - name: Get changed .sql files in mimic-iv concepts folder
         id: get_files_to_lint
         shell: bash
         run: |
-          # Compose list of changed SQL files under mimic-iv/concepts and export to step output
-          raw="${{ steps.get_file_changes.outputs.files_modified }} ${{ steps.get_file_changes.outputs.files_added }}"
-          # Check for mimic-iv SQL files which may have changed
-          filtered="$(printf '%s' "$raw" | tr -s ' ' '\n' | grep -E '^mimic-iv/concepts/.*[.]sql$' || true)"
-          # Turn this into a space separated list for the next step
-          files="$(printf '%s' "$filtered" | tr -s '\n' ' ')"
+          # Added/modified (--diff-filter=AM) SQL files on the PR branch since
+          # it diverged from the base branch, restricted to mimic-iv/concepts.
+          files="$(git diff --name-only --diff-filter=AM \
+            "origin/${{ github.base_ref }}...HEAD" -- 'mimic-iv/concepts/' \
+            | grep -E '[.]sql$' | tr '\n' ' ' || true)"
           echo "lintees=${files}" >> "$GITHUB_OUTPUT"
 
       - name: Lint SQL files