github: update checkout action

Gets rid of the warning:

  Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
         - macos-latest
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Install IO::Pty
       if: matrix.os == 'ubuntu-latest'
       run: sudo apt-get update -y && sudo apt-get install -y libio-pty-perl