🔒 Pin GitHub actions by commit SHA (#2246)

.github/workflows/test-backend.yml

@@ -14,13 +14,13 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
       - name: Set up Python
-        uses: actions/setup-python@v6
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with:
           python-version: "3.10"
       - name: Install uv
-        uses: astral-sh/setup-uv@v7
+        uses: astral-sh/setup-uv@37802adc94f370d6bfd71619e3f0bf239e1f3b78 # v7.6.0
       - run: docker compose down -v --remove-orphans
       - run: docker compose up -d db mailcatcher
       - name: Migrate DB
@@ -31,7 +31,7 @@ jobs:
         working-directory: backend
       - run: docker compose down -v --remove-orphans
       - name: Store coverage files
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
         with:
           name: coverage-html
           path: backend/htmlcov