Update actions/checkout to v4

Author: finestructure

.github/workflows/ci.yml

@@ -28,6 +28,6 @@ jobs:
       image: swift:5.10.0-amazonlinux2
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Run tests
         run: swift test

.github/workflows/deploy.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           # Fetch all history to ensure the version number (tag) is resolved to create the
           # version info during the build step.