Switch to actions/checkout@v4

Using default branch is not that great idea.

.github/workflows/perl.yml

@@ -30,7 +30,7 @@ jobs:
       image: perldocker/perl-tester:${{ matrix.perl-version }}
 
     steps:
-      - uses: actions/checkout@main
+      - uses: actions/checkout@v4
       - run: git config --global --add safe.directory "$GITHUB_WORKSPACE"
       - run: perl -V
       - run: cpanm --notest --installdeps --verbose .