Bump actions/checkout from v2.3.0 to v2.3.1 (#33)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/build.yml

@@ -43,7 +43,7 @@ jobs:
         shell: bash
 
       - name: Checkout the "hidden" branch
-        uses: actions/checkout@v2.3.0
+        uses: actions/checkout@v2.3.1
         with:
           ref: hidden