[test.yml] Bump actions/checkout.

Author: lgarron

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Install ImageMagick
         run: brew install imagemagick
       - name: make test