fix: install detect-secrets before prompt injection scan in CI

Author: john-walkoe

.github/workflows/secret-scan.yaml

@@ -65,7 +65,9 @@ jobs:
         uses: astral-sh/setup-uv@v3
 
       - name: Install dependencies
-        run: uv sync
+        run: |
+          uv sync
+          uv pip install detect-secrets
 
       - name: Run prompt injection detection
         run: |