Pin workflow hashes (#232)

To comply with the new org-wide policy.

Author: di

.github/workflows/ci.yml

@@ -17,8 +17,8 @@ jobs:
     name: ${{ matrix.name }}
     steps:
       - name: Check out repository
-        uses: actions/checkout@v5
-      - uses: actions/setup-python@v5
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
         with:
           python-version-file: '.python-version'
           cache: 'pip'