CI: Use GH Actions checkout@v4

Author: olleolleolle

.github/workflows/ci.yaml

@@ -27,7 +27,7 @@ jobs:
             ruby: '3.2'
     runs-on: ${{ matrix.os }}-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}
@@ -39,7 +39,7 @@ jobs:
   valgrind:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: '3.1'
@@ -55,7 +55,7 @@ jobs:
         ruby: ['jruby-9.3', 'jruby-9.4', 'truffleruby']
     runs-on: ${{ matrix.os }}-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}
@@ -73,7 +73,7 @@ jobs:
         ruby: ['ruby-head', 'jruby-head']
     runs-on: ${{ matrix.os }}-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}