Pin actions/checkout to a5ac7e5 (#159)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://togithub.com/actions/checkout) | action |
pinDigest | -> `a5ac7e5` |

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.github/workflows/links.yaml

@@ -14,7 +14,7 @@ jobs:
     timeout-minutes: 2
     steps:
       - name: Checkout source
-        uses: actions/checkout@v4
+        uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29 # v4
 
       - name: Check links
         uses: paddyroddy/.github/actions/links@v0