security: pin version of py-actions/py-dependency-install

Remeidates: https://docs.zizmor.sh/audits/#impostor-commit
Version: https://github.com/py-actions/py-dependency-install/releases/tag/v4.0.0

Author: andrewpollack

.github/workflows/checks.yml

@@ -6,14 +6,15 @@ permissions:
 
 jobs:
   Run-Markdown-Checks:
+    name: Run Markdown Checks
     runs-on: ubuntu-24.04
     steps:
       - name: checkout
         uses: actions/checkout@v4
         with:
           persist-credentials: false
       - name: Install Python dependencies
-        uses: py-actions/py-dependency-install@v4
+        uses: py-actions/py-dependency-install@9c419aa98bfb42280bdae2b0a736befd9b01e3b1 # v4
         with:
           path: "tools/requirements.txt"
           update-pip: "false"