CI: Use current version of checkout@v4

Author: okurz

.github/workflows/ci-tests.yaml

@@ -25,7 +25,7 @@ jobs:
             perl: latest
     name: 🐪 Perl ${{ matrix.perl }} on ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: shogo82148/actions-setup-perl@v1
         with:
           perl-version: ${{ matrix.perl }}