[codex] Pin GitHub Actions workflow references (#15828)

Pin floating external GitHub Actions workflow refs to immutable SHAs.

Why are we doing this? Please see the rationale doc:
https://docs.google.com/document/d/1qOURCNx2zszQ0uWx7Fj5ERu4jpiYjxLVWBWgKa2wTsA/edit?tab=t.0

Did this break you? Please roll back and let hintz@ know

.github/workflows/bazel.yml

@@ -48,7 +48,7 @@ jobs:
     name: Local Bazel build on ${{ matrix.os }} for ${{ matrix.target }}
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
       - name: Set up Bazel CI
         id: setup_bazel
@@ -85,7 +85,7 @@ jobs:
       - name: Save bazel repository cache
         if: always() && !cancelled() && steps.setup_bazel.outputs.cache-hit != 'true'
         continue-on-error: true
-        uses: actions/cache/save@v5
+        uses: actions/cache/save@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5
         with:
           path: |
             ~/.cache/bazel-repo-cache
@@ -106,7 +106,7 @@ jobs:
     name: Bazel clippy on ${{ matrix.os }} for ${{ matrix.target }}
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
       - name: Set up Bazel CI
         id: setup_bazel
@@ -136,7 +136,7 @@ jobs:
       - name: Save bazel repository cache
         if: always() && !cancelled() && steps.setup_bazel.outputs.cache-hit != 'true'
         continue-on-error: true
-        uses: actions/cache/save@v5
+        uses: actions/cache/save@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5
         with:
           path: |
             ~/.cache/bazel-repo-cache