ci: name the exact checkout tag in the pin comment

Author: wangauone

.github/workflows/presubmit-tests.yml

@@ -25,7 +25,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
       - name: Install Gemini CLI
         run: npm install @google/gemini-cli