Bump actions/checkout from 3 to 4

Author: oschulz

.github/workflows/ci.yml

@@ -43,7 +43,7 @@ jobs:
             os: windows-latest
             arch: x64
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.version }}
@@ -65,7 +65,7 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v1
         with:
           version: '1'