Bump actions/checkout from 2 to 3 (#144)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.

Author: dependabot[bot]

.github/workflows/CI.yml

@@ -28,7 +28,7 @@ jobs:
         arch:
           - x64
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.version }}
@@ -44,7 +44,7 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
           version: '1'