Use checkout action v3 in CI (#128)

Author: jishnub

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
         arch:
           - x64
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.version }}