[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/v8-canary.yml

@@ -38,10 +38,10 @@ jobs:
       v8_version: ${{ steps.v8_version.outputs.version }}
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
       - name: Set up Python
-        uses: actions/setup-python@v6
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6
         with:
           python-version: "3.12"
 
@@ -72,13 +72,13 @@ jobs:
             target: aarch64-unknown-linux-musl
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
       - name: Set up Bazel
-        uses: bazelbuild/setup-bazelisk@v3
+        uses: bazelbuild/setup-bazelisk@6ecf4fd8b7d1f9721785f1dd656a689acf9add47 # v3
 
       - name: Set up Python
-        uses: actions/setup-python@v6
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6
         with:
           python-version: "3.12"
 
@@ -126,7 +126,7 @@ jobs:
             --output-dir "dist/${TARGET}"
 
       - name: Upload staged musl artifacts
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7
         with:
           name: v8-canary-${{ needs.metadata.outputs.v8_version }}-${{ matrix.target }}
           path: dist/${{ matrix.target }}/*