CI: update actions/checkout

Signed-off-by: Andrei Horodniceanu <a.horodniceanu@proton.me>

Author: the-horo

.github/workflows/d.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: dlang-community/setup-dlang@v2
 
     - name: 'Build & Test'