ci: bump actions/checkout to v4 (#1595)

Hey ! GitHub‑hosted runners now use Node 20, so checkout v4 is required
This PR updates all workflows to actions/checkout@v4 , no functional
changes expected

Author: dizer-ti

.github/workflows/riscv.yml

@@ -42,7 +42,7 @@ jobs:
           cache-on-failure: true
       - uses: taiki-e/install-action@nextest
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: recursive