ci(docling_serve): Use commit hashes for pinning actions

Author: bogdankostic

.github/workflows/docling_serve.yml

@@ -39,10 +39,10 @@ jobs:
         python-version: ["3.10", "3.14"]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
         with:
           python-version: ${{ matrix.python-version }}
 
@@ -69,7 +69,7 @@ jobs:
 
       - name: Upload coverage comment to be posted
         if: matrix.python-version == '3.10' && runner.os == 'Linux' && github.event_name == 'pull_request' && steps.coverage_comment.outputs.COMMENT_FILE_WRITTEN == 'true'
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: coverage-comment-docling_serve
           path: python-coverage-comment-action-docling_serve.txt