[codex] Fully qualify hash-pins in GitHub Actions (#21436)

This builds on top of https://github.com/openai/codex/pull/15828 by
ensuring that hash-pinned actions with version comments are fully
qualified, rather than referencing floating/mutable comments like "v7".
This makes actions management tools behave more consistently.

This shouldn't break anything, since it's comment only. But if it does,
ping ww@ 🙂

.github/workflows/sdk.yml

@@ -13,7 +13,7 @@ jobs:
     timeout-minutes: 10
     steps:
       - name: Checkout repository
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
       - name: Install Linux bwrap build dependencies
         shell: bash
@@ -28,7 +28,7 @@ jobs:
           run_install: false
 
       - name: Setup Node.js
-        uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6
+        uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0
         with:
           node-version: 22
           cache: pnpm
@@ -115,7 +115,7 @@ jobs:
       - name: Save bazel repository cache
         if: always() && !cancelled() && steps.setup_bazel.outputs.cache-hit != 'true'
         continue-on-error: true
-        uses: actions/cache/save@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5
+        uses: actions/cache/save@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
         with:
           path: |
             ~/.cache/bazel-repo-cache