Update actions/checkout action to v6 (llvm#171065)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://redirect.github.com/actions/checkout) |
action | major | `v5.0.0` -> `v6.0.1` |

Author: renovate-bot

.github/workflows/release-sources.yml

@@ -108,7 +108,7 @@ jobs:
       attestations: write
     steps:
       - name: Checkout Release Scripts
-        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
         with:
           sparse-checkout: |
             .github/workflows/upload-release-artifact