Update actions/checkout

Author: mernen

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     - uses: earthly/actions-setup@v1
       with:
         version: "^0.8"
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v6
     - name: Test all supported versions
       run: earthly --ci +test
     - name: Test latest releases