ci(deps): pin GitHub Actions to commit SHAs (#8065)

Every third-party GitHub Action in the workflows is now pinned to a full
commit SHA instead of a floating major tag, closing a supply-chain gap
where a mutable tag like `@v6` could be force-pushed to point at
malicious code. Seven actions were already SHA-pinned; this brings the
remaining first-party `actions/*` and `astral-sh/setup-uv` references in
line.

## Changes
- Pinned all previously tag-referenced actions to their current commit
SHA with the exact release as a trailing comment (the format Dependabot
reads and updates): `actions/checkout` → `v6.0.3`,
`actions/setup-python` → `v6.2.0`, `actions/github-script` → `v9.0.0`,
`actions/upload-artifact` → `v7.0.1`, `actions/download-artifact` →
`v8.0.1`, `actions/cache/{restore,save}` → `v5.0.5`,
`actions/configure-pages` → `v6.0.0`, `actions/deploy-pages` → `v5.0.0`,
`actions/upload-pages-artifact` → `v5.0.0`,
`actions/create-github-app-token` → `v3.2.0`, and `astral-sh/setup-uv` →
`v7.6.0`.
- Applied across all workflow files plus the `uv_setup` composite
action; local same-repo references (`./.github/workflows/_*.yml`,
`./.github/actions/uv_setup`) left as path refs since they resolve from
the same commit.

.github/workflows/bench.yml

@@ -15,7 +15,7 @@ jobs:
       run:
         working-directory: libs/langgraph
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - id: files
         name: Get changed files
         uses: Ana06/get-changed-files@25f79e676e7ea1868813e21465014798211fad8c # v2.3.0
@@ -30,7 +30,7 @@ jobs:
       - name: Install dependencies
         run: uv sync --group test
       - name: Download baseline
-        uses: actions/cache/restore@v5
+        uses: actions/cache/restore@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
         with:
           key: ${{ runner.os }}-benchmark-baseline
           restore-keys: |
@@ -57,7 +57,7 @@ jobs:
             echo EOF
           } >> "$GITHUB_OUTPUT"
       - name: Annotation
-        uses: actions/github-script@v9
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
         env:
           CHANGED_FILES: ${{ steps.files.outputs.added_modified_renamed }}
           BENCHMARK_OUTPUT: ${{ steps.benchmark.outputs.OUTPUT }}