[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/rust-release-prepare.yml

@@ -18,7 +18,7 @@ jobs:
     if: github.repository == 'openai/codex'
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           ref: main
           fetch-depth: 0
@@ -43,7 +43,7 @@ jobs:
           curl --http1.1 --fail --show-error --location "${headers[@]}" "${url}" | jq '.' > codex-rs/models-manager/models.json
 
       - name: Open pull request (if changed)
-        uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 # v8
+        uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 # v8.1.0
         with:
           commit-message: "Update models.json"
           title: "Update models.json"